Benfica have warned Manchester United to increase their offer for Enzo Perez if they are serious about signing him. The Portuguese club are holding firm and are adament they will not sell their star unless his 25m release clause is met, O Jogo reports. Valencia lodged a 20m bid for the 28-year-old star but had their offer instantly turned down by Benfica president Luis Felipe Vieira, who is determined to keep hold of the player. Man United have also been in discussions with Benfica and are considering meeting the player’s valuation as new boss Louis van Gaal desperately looks to bolster the club’s flagging squad. The Red Devils are understood to have offered 16m for the player, which was dismissed out of hand by Benfica.