The San Francisco 49ers will finish their preseason schedule Friday against the Las Vegas Raiders at Allegiant Stadium.

One of the reasons for optimism about the 49ers entering the offseason revolved around their lack of high-profile roster turnover. They lost a couple key players, but their starting groups were on track to look mostly the same as a last year when they went to the Super Bowl.

Now, with the preseason winding down and the proverbial rubber rapidly approaching the metaphorical road, things have changed a little bit. Contract talks, injury issues and training camp performances have pushed a handful of starting roles into a more uncertain realm.

Here are five starting spots that are still question marks as the 49ers get set to wrap up their preseason Friday night:

Strong safety

Talanoa Hufanga tore his ACL in Week 11 last season. Early offseason estimates indicated he'd return at some point during training camp, paving the way for the All-Pro to suit up in the season opener. He's been ruled out of the preseason finale, and he's yet to even return to practice. If he's unable to get on the practice field with enough ramp up to play in Week 1, the 49ers could wind up starting George Odum at strong safety in their regular season opener.

Left tackle

Trent Williams holding out for all of training camp and the preseason wasn't on our offseason Bingo card. There was never really any pessimism that Williams and the 49ers wouldn't come to an agreement on a new contract for the 36-year-old, but we now have to live in the reality where he's not in uniform for the opener. Jaylon Moore has filled in for Williams throughout camp and the preseason, so he'll be the frontrunner to snag the starting LT job if Williams isn't there for Week 1.

Wide receiver

It's a little less of a surprise that the Brandon Aiyuk contract saga has lasted this long. However, it's still a wrinkle the 49ers don't want to be ironing out this late in the calendar. Without Aiyuk, the 49ers receiving corps becomes a massive question mark. Jauan Jennings figures to step into the starting job alongside Deebo Samuel. Who fills in as the third receiver, on the other hand, is a much bigger question. Journeyman Chris Conley and inexperienced rookies Ricky Pearsall and Jacob Cowing headline the potential option. Danny Gray and Ronnie Bell are also potentially in that mix.

Nickel cornerback

Finally, a good problem! The 49ers haven't landed on a nickel cornerback yet because they actually have a few good options. They could have Isaac Yiadom outside and move Deommodore Lenoir into the slot. They might also start rookie Renardo Green in the slot and have Lenoir stay outside. Rock Ya-Sin has had a nice preseason and may be in the mix, but the more likely outcome is one of Yiadom or Green lining up with Lenoir and Charvarius Ward against the Jets. This decision may come down to the wire just ahead of the opening kickoff.

Sam linebacker

Technically Sam LB and nickel CB can't both be starting jobs, but work with us. The Sam LB starts in the team's base defense. Veteran Demetrius Flannigan-Fowles appears to be the frontrunner there, but the LB corps has shined in the preseason. Dee Winters, Jalen Graham and Curtis Robinson could all conceivably wind up as the third starting LB in the team's 4-3 base defense.

This article originally appeared on Niners Wire: 49ers have uncertainty at 5 starting spots heading into preseason finale