Manchester United defender Matthijs de Ligt sustained an injury at the structure by his side and gave a goal against Brentford.
Although De Ligt clearly had pain after bumping into Bryan Mbeumo, the game was allowed to continue, where Kevin was damaged to put Brentford in the front in the 33rd minute.
Shortly thereafter De Ligt had to be replaced, with Harry Maguire replacing it.
It is the second time that such an incident has occurred at De Ligt against Brentford this season.
In October the Dutchman was left with a bloody head after a collision with damage in Old Trafford.
On that occasion, Ethan Pinnock scored for Brentford, while De Ligt was not off the field and received treatment.
Erik ten Hag, when the leadership of United, received a yellow card for his furious protests from officials.
In that game, United won 2-1 when they were right through Alejandro Garnacho before Rasmus Hojlund got the winner.
On Sunday, however, it was Brentford who took all three points when they won 4-3.
Mason Mount had set United in front before Luke Shaw Brentford saw his own goal.
Damage placed Brentford at the front in controversial circumstances and he added a different goal in the second half before Yoane Wissa made it 4-1.
United threatened to organize a comeback when Garnacho and Amad Diallo scored, but Brentford held on to achieve all three points.
The result leaves United in 15th place in the Premier League – they suffered 16 defeats this season.
United will close their competition campaign with competitions at home at West Ham, road to Chelsea and at home at Aston Villa.
Their most important focus will be on the Europa League, with the side of Ruben Amorim a 3-0 lead of their first stage of their semi-final against Athletic Bilbao.
United could be confronted with Tottenham in a full-English final-the team of Ange Postecoglou leads 3-1 of the first stage against Bodo/Glimt.