In the best part of seven years, Manchester United have won a lone trophy. Casemiro, in contrast, has three Champions Leagues since Jose Mourinho’s United lifted the Europa League in 2017. The Brazilian has a couple of La Liga titles in that time, too, plus the Uefa Super Cup, Club World Cup and Copa America. Perhaps it was no surprise, therefore, that the 2023 Carabao Cup came courtesy of a goal and a man-of-the-match performance from Casemiro in the final.

There is a theory, often promulgated by men such as Mourinho with sizeable medal collections and a sense of their own superiority, that football can be divided into two categories: winners and others. There is no doubt which bracket contains Casemiro and his celebrations at Wembley, his evident delight, was proof he did not just delight in winning the Champions League.

And yet the subsequent 14 months have been a chastening period for one of the most decorated players of his generation, perhaps an illustration for United that success is not as simple as just buying people with a history of securing silverware. Casemiro had being on the victorious side in nine consecutive major finals in which he played, until United lost a Manchester derby in the FA Cup at Wembley last summer. Casemiro has never finished outside the top four in a season in Europe; United have never been in it all campaign and could lose seventh place on Sunday.

For Casemiro, the time since the 2023 Carabao Cup final has brought injuries, suspensions and questions if he is in decline. He has collected 14 yellow cards and two reds, with Erik ten Hag sometimes substituting him to spare him a more inglorious early exit. The sense is that it has become ever more apparent why Real Madrid were willing to accept United’s overtures, breaking up a defining midfield with Luka Modric and Toni Kroos but pocketing £63m for a player in his thirties.

If the accusation is that Casemiro is doing too little to shield United’s ever-changing back fours, Ten Hag came to the defence of one of his biggest buys. “I think we needed the [No] 6 when I arrived here and last season Casemiro was fantastic,” he said.

So far, so uncontroversial: Casemiro equalled a career-best with seven goals in his debut campaign at Old Trafford and Ten Hag added: “I don’t think he ever scored so many goals as well but as a 6, as a holding midfielder, as a strategist, he was so important for the team. This season he struggled with some bad injuries, which he never had in his career, but I know he is such a winner. You see his career: he always won. Everywhere where he, there will be success and I trust he will give us also this success and I know he will need games, he will be better and I’m very confident about him. He is a fighter, why he also won big trophies, he is a personality, and he’s a very important player.”

The alternative argument is that the issue is not with his mentality, but his mobility. At Wembley after the Carabao Cup final, Casemiro said in his native Portuguese: “I go after the ball like it’s a plate of food.” And if his less-than-svelte physique suggests that is a different problem, his deteriorating disciplinary record is a consequence of Casemiro seeming to go to ground more frequently in desperate bids to halt quicker players.

United’s absurdly open games – and their opponents have had 107 shots in their last four matches alone and at least 20 in nine of their last 20 Premier League games – reflects the lack of protection provided in midfield. It feels an indictment of both Casemiro and Ten Hag. Even when the Brazilian is paired with the prodigy Kobbie Mainoo, United have conceded the most shots in Europe’s top five leagues in 2024. Last year, there seemed more structure and solidity. But then Casemiro looked a player still at the peak of his powers, not one past them.

Maybe the Carabao Cup final against Newcastle will forever remain the high point of his time at Old Trafford. Ten Hag could be forgiven for reminiscing. “Not only that game, also how we achieved Champions League [qualification], he was such an important factor and that day he makes a difference with his header and how we read and control the game.”

Now United are the team with no control. Casemiro is the winner whose season could end with him adding the FA Cup to his roll of honour, or with United failing to qualify for Europe altogether, a humiliation for a man accustomed to conquering it. Will Casemiro win because he has always won? Or struggle because he is a lesser force now? For now, Ten Hag is trusting in his track record and ignoring the warning signs.