The Red Devils suffered a disappointing 2-1 defeat to the Cottagers in the Premier League last weekend, with Alex Iwobi scoring a 97th-minute winner at Old Trafford.
After the match, Fulham uploaded a video on TikTok of Fernandes falling to the ground and clutching his leg following a challenge from Sasa Lukic.
As play continued without a free kick being awarded, the Red Devils captain swiftly got back up onto his feet to make himself available for a pass on the edge of the penalty box.
The 15-second clip is accompanied with comical music and the caption «So glad he's OK» as well as the eye-rolling emoji.
Ten Hag was made aware of Fulham's post during a press conference on Thursday, and although at the time he had not seen the clip, he has encouraged the Cottagers to apologise for the «totally out of order» video.
Asked directly about Fulham's video, Ten Hag told reporters: «I didn't know this, but if they did it I would say it is not right.
»It is absolutely not right that a club makes such a statement, because it is totally out of order and they were wrong so they should apologise for this."
Fernandes emerged as a doubt for Man United's FA Cup fifth-round tie against Nottingham Forest on Wednesday, and according to The Telegraph, Man United sources claim that the incident in which Lukic caught the 29-year-old was the moment that he sustained his injury.
Man United's No.8 was eventually fit to start the contest at the City Ground and his free kick set up Casemiro to score an 89th-minute winner in a 1-0 victory, setting up a quarter-final clash with Liverpool.
However, Fernandes
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