Manchester United's physios have been accused of missing a potentially serious hamstring injury when checking on the fitness of Casemiro ahead of their clash with Liverpool last weekend.
The midfielder missed the 4-3 FA Cup quarter-final thriller at the weekend with the issue, and he has since withdrawn from the Brazil squad that will face England and Spain this week.
Erik ten Hag's hand was then forced, so Scott McTominay started alongside Kobbie Mainoo in a midfield two at Old Trafford.
In the day prior to the showdown with their bitter rivals, Casemiro is believed to have complained about pain in his hamstring - an issue which has already kept him out for three months this season, and almost required surgery.
Despite that though, the Man United medical team ruled him fit to play against Liverpool, diagnosing no significant problems after an examination.
However, Brazilian outlet Trivela claim that Casemiro was not satisfied with this conclusion, and went to seek a second opinion with his own personal doctor in Barcelona.
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After consulting with his doctor, Casemiro was told that he had sustained a minor injury, and it could become a big problem if he attempts to play through it, suggesting he should sit out the next few weeks to avoid aggravating it and turning it into a more serious issue than it currently is.
Casemiro ended up being a late casualty from the side which faced Liverpool, with the club then confirming that the player had picked up a "muscle injury".
After sustaining an ankle problem in October, Casemiro returned for just 45 minutes in their EFL Cup defeat at home to Newcastle United, picking up a serious hamstring injury in that 3-0 defeat.
That would then keep the Brazilian out from the start of November until mid-January, as he would not feature again until the FA Cup tie at Newport County.
Casemiro has featured in the nine games since, but questions remain about how serious this more recent problem is, and whether it is a recurrence of a previous injury.
At present, the 32-year-old is in contention to return when Man United are back in action against Brentford on March 30, with the three-week break set to give ample time for the issue to settle down.