Benfica president Luis Filipe Veira has made it clear that any club trying to sign Axel Witsel will have to meet the players release clause which stands at a staggering £31million.
Goal.com has reported that Manchester United have been long-term admirers of the powerful central midfielder who only made the move to Portugal last season when he signed from Standard Liege for just £5.4million.
"Every club knows what his release clause is," Vieira told Antena 1, as reported ongoal.com. "If they come here and pay that fee, then there is nothing that we can do. We are very happy with Witsel and we do not think about selling him."
However, he impressed in his debut season with Benfica and the club are now desperate to stave off interest from some of the biggest clubs in Europe by revealing that he will not be sold for less than £31million.
The report suggests that AC Milan and Manchester United have both been strongly linked with Witsel in recent months after an impressive season with Benfica in which he starred in both the Champions League and then the Europa League.
United boss Sir Alex Ferguson would have been able to check on the progress of the 23-year-old last season when he appeared against Chelsea in the group stages of the Champions League.
The Premier League runners-up have already signed two new midfielders in Nick Powell and Shinji Kagawa but they are still seeking a player who can win, and then distribute the ball in the heart of the pitch.
Darren Fletcher was the man often given the task but there is still no confirmed date for his comeback from a bowel condition that saw him ruled out of action for the vast majority of last season.
Anderson has also failed to make the role his own and there has been speculation that Ferguson would continue to look for more options in midfield over the summer months.