The return of Isaiah Thomas may be the biggest midseason acquisition by any NBA team this winter, and that’s no small concession, considering the Cleveland Cavaliers remain among the Eastern Conference elite. They’re vying for a fourth straight Finals appearance, and they already feature the only player who has proven capable of disrupting a Golden State Warriors dynasty in the making.

LeBron James is still Cleveland’s superhero for now, but whether Thomas becomes the trusty sidekick that Kyrie Irving was for the Cavs these past few years could determine the fate of the NBA.

Thomas will make his Cavaliers debut off the bench against the Portland Trail Blazers on Tuesday night, playing for the first time since a hip injury ended his season prematurely for the Boston Celtics in the conference finals this past May. He will be on a minutes restriction and will sit against the East-leading C’s on Wednesday, likely because the adrenaline of a return to Boston combined with his rustiness would only add undue stress on a player Cleveland will need to make it back to the Finals.

We shouldn’t expect much from Thomas on Tuesday, or even in the coming weeks, but you can bet the Cavaliers are banking on him to regain his form as one of the league’s top playmakers by playoff time.

The organization traded Irving — the 25-year-old four-time All-Star point guard who helped deliver the franchise’s only title — for Thomas, Jae Crowder, Ante Zizic and a first-round pick from the Brooklyn Nets. And while the Nets pick may someday be the biggest prize in that package, the 5-foot-9 Thomas played no small part in convincing the Cavs to trade a prized player to a conference rival.

Thomas was a top-five MVP candidate, a second-team All-NBA selection and one of the game’s four most impactful guards last season. Leading the Celtics to a No. 1 seed, Thomas’ 28.9 points per game ranked third behind only superstars Russell Westbrook and James Harden in 2016-17. His true shooting percentage (62.5 percent) also made him one of the league’s most efficient scorers, and his 5.9 assists per game completed an offensive game that left him among the league leaders in almost every advanced statistical category. These are numbers even Irving could not replicate a season ago.

Of course, Irving had to share the stage with LeBron. That’s an adjustment that took them at least a season to fully understand and ultimately led to their breakup another two years later. Now, Thomas must push the pedal to the floor on that process, and while he expects to adjust to life with LeBron “quicker than somebody else could,” there’s no doubt there will be a learning curve on top of his reintroduction to NBA basketball. No pressure, but the future of the franchise just may depend on it.

Even then, it might not be enough.

Despite Thomas being sidelined and the Cavs relying on Jose Calderon as their starting point guard, they’ve been every bit the offensive juggernaut they were with Irving last season, if not more so. They’ve scored 111.2 points per 100 possessions this season, as opposed to 110.9 a year ago — both offensive ratings good for third in the league. It’s their defense that has slipped from merely below average last season to third-worst through three months (108.7 points allowed per 100 possessions).

The margin for error is narrower now, what with Irving’s Celtics and the Toronto Raptors holding the East’s top two seeds, and Thomas is of little to no help defensively — less for a lack of effort than an inability to stop larger guards. This is a problem. The Cavs will hope adding Thomas’ dynamic scoring can lift their offense to a historically great stratosphere, which could be enough to carry the day against Boston and Toronto, but means little if their end goal is to once again take down a Warriors team that has scored at historic levels for three years running and also owns the NBA’s top defense.

The Cavs are deeper now, with Dwyane Wade running the second unit, Kyle Korver still sharp-shooting and Jeff Green playing well in a limited role. But they’ll be no match for the Warriors without another creator to share the load with LeBron, and we’re still not sure if Thomas can be that guy this season.

Ideally, Thomas’ return would unlock the Jae Crowder that two-way advanced stats came to love in Boston and allow Cleveland coach Tyronn Lue to field lineups with more defensive-oriented players, rather than fill the offensive void left by Irving with multiple scorers to the detriment of the defense.

For example, a small lineup with Kevin Love at center, LeBron, Crowder, Wade and J.R. Smith has been OK offensively and dreadful defensively. Likewise, a big lineup with Tristan Thompson at center, Love, LeBron, Crowder and Smith has been woeful on both ends. Pair Thomas with LeBron as the primary ball-handlers, surround them with Crowder, Thompson and whoever, and maybe the Cavaliers find a five-man unit that can still score at a break-neck pace and begin to defend at a respectable level.

So long as the Cavs had LeBron and Irving on the floor during the playoffs last season, they were an almost unstoppable offensive force, while being flexible enough for a myriad of players to patch together a defense that nearly made the Finals a 2-2 series this past June. Can Thomas provide the same stability? It’s hard to imagine the guy who carried the Celtics through fourth quarters last season (and assisted on more Crowder field goals than anyone) couldn’t give the Cavaliers a similar boost.

Except, we don’t know if that’s the guy the Cavs are getting, and not just because of the injury. How much did a Brad Stevens-designed offense around Thomas as the primary option lend to his success? Thomas can shoot, no doubt, which makes him a threat off the ball, but much of his greatness last season was predicated upon his ability to get to the rim. Can he still do that on a rehabbed right hip? Or will the threat of bumping much larger bodies in the paint take a physical and mental toll on him?

These are the questions the Cavs must answer. And fast. They’ve been straddling the line between building around LeBron and preparing for a future without him, and Thomas’ success could have an impact on which direction the front office leans as soon as the trade deadline next month. The Cavs have that Nets pick, which currently holds the 10th-best lottery odds, and that may be enough (with salary filler) to pry Marc Gasol or DeAndre Jordan away from the Memphis Grizzlies or L.A. Clippers.

A healthy Thomas with LeBron, Love and All-Star X seems like a contender this year and beyond. Maybe that’s enough to persuade LeBron to stay in Cleveland as a free agent this coming summer.

On the other hand, if the Cavs aren’t convinced Thomas can be a viable Kyrie replacement, they may keep the Brooklyn pick as insurance for an uncertain future. Without Thomas playing anywhere close to the level he reached in Boston, Cleveland may not survive the East, let alone the Finals, so what sense is there pushing their only real trade chip in now when a rebuild could be fast approaching?

Without Thomas at full strength, LeBron might soon become convinced the Cavs can never return to the heights they reached in 2016 and bolt for a more promising roster elsewhere around the league.

Of course, Thomas can leave this summer, too, so he will have extra incentive to prove his value in the coming weeks and months. He hasn’t backed off his “back up the Brinks truck” demands for a max contract, and for the Cavaliers to invest that type of money in a 5-foot-9 point guard who will turn 30 next season, they are going to need to be convinced quickly that he’s still as good as advertised. We shall see how Thomas balances that financial end goal with his newest role as a superstar sidekick.

So, Thomas’ return doesn’t just represent a promising midseason acquisition. His success now could mean the difference between the Cavs contending for the foreseeable future or waving goodbye to an unprecedented era. That’s a heavy burden to carry on a bum hip. Yet, if anyone can shoulder that load, it’s the diminutive 60th overall pick who submitted one of the all-time great seasons a year ago.

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Ben Rohrbach is a contributor for Yahoo Sports. Have a tip? Email him at rohrbach_ben@yahoo.com or follow him on Twitter! Follow @brohrbach