The Mirror says Ferguson has given the Spaniard every chance to fill the jersey at Old Trafford but doubts about his ability to handle the physical side are growing.
And the shrewd United chief has asked supremo David Gill and the club's American owners to fund a buy for a genuine number one.
United splashed out on De Gea when Fergie took a chance on his potential and brought him in from Atletico Madrid, but his fragility under pressure has not gone away.
De Gea is often targeted by the opposition when it comes to set pieces and high balls and his sheer lack of physique is a problem.
Ferguson's spies have been checking on alternatives for weeks but now the United boss is in serious discussions with Gill and the Glazers about a kitty for a new man.