Louis van Gaal admitted it will be difficult to persuade David de Gea to stay at Manchester United amid doubt if he will ever play for the club again.
De Gea was given a huge ovation by United fans when he was substituted with a hamstring injury in the 1-1 draw with Arsenal and then on a lap of honour after the final whistle.
But manager Van Gaal feels the allure of Real Madrid, who want to sign the 24-year-old, could be too great for a Spaniard to resist.
United have offered De Gea, whose current contract expires in 2016, a lucrative new deal and Van Gaal has warned the former Atletico Madrid player he may not be loved in such a way at the Bernabeu.
The Dutchman said in a news conference: "I analyse his position and then I say he is Spanish, he is a Spanish international, still behind [Iker] Casillas [for the national team], now a Spanish club is coming [in for him], his girlfriend is Spanish, his father and mother come every week or every two weeks here [from Spain] so it is difficult.
"I don't think I can persuade him. He knows everything what he has at the moment in Manchester United so I don't have to say something in benefit of Manchester United because he can feel it every day. You have seen the fans: unbelievable. When he is going, he is losing that. Here he has a lot of credits. He has to decide."
Van Gaal claimed not to know if Real have submitted an offer for De Gea, who joined United in 2011, and suggested he does not think the goalkeeper will recover in time to face Hull next week.
"His injury is a hamstring injury so it shall be difficult to play but you never know," he added.
Radamel Falcao, who has spent the season on loan at Old Trafford, seemed to be waving farewell to the crowd when he was substituted by Van Gaal, denied a decision has been reached about the Colombian's future.