Interim Manchester United coach Ralf Rangnick has said forward Anthony Martial should have the courage to submit a formal transfer request if he wants to leave the club January.

Martial's agent, Philippe Lamboley, said on Friday that the 26-year-old wants to leave Old Trafford in the next transfer window.

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But the news came as a surprise to Rangnick, who insists Martial has not approached him or the club about his plans.

"I don't communicate with agents via the media and press," Rangnick said. "The player hasn't spoken with me or us about it.

"To be honest, what his agent says via the media is not of that much interest to me. It should be the player. If he really has the wish to go to another club it should be the player who informs either the board or myself. I have never spoken about a player via the media and via agents."

Lamboley suggested Martial wants to leave because of a lack of regular games.

The striker has not played since the 2-0 win over Villarreal under caretaker coach Michael Carrick, but Rangnick hit back by claiming he has not featured recently after telling staff he is injured.

"After the final training session before the Crystal Palace game, after having trained with the team, he informed the doctor and the medical department that he would not be available because the pain in his knee is too big," Rangnick said.

"We have to wait and see. Maybe he can train again [before playing Brentford on Tuesday] but I have to speak to the doctor first."

United are dealing with a COVID-19 outbreak in the build up to the trip to Brentford on Tuesday. Rangnick's team have won back-to-back league games with two consecutive clean sheets to move up to fifth in the table.

"I saw the Brentford game against Watford and they are another high intensity team, maybe more physical even than Norwich," Rangnick added.

"We need to be aware and prepare for that different level of intensity."