David de Gea has technical flaws in his goalkeeping and his form has been beset by a "consistency of errors", according to Mark Bosnich.
The 29-year-old made a calamitous mistake when he parried Mason Mount's shot into the net during Manchester United's 3-1 FA Cup semi-final defeat to Chelsea on Sunday.
Ole Gunnar Solskjaer has backed his under-fire goalkeeper but Bosnich reckons it will be a huge call as to whether to install back-up Sergio Romero instead for the rest of the season.
"I spoke some weeks ago after that error against Tottenham and I spoke about it from a technical point of view how he seems to be pushing all his balance going forward with his feet," former United goalkeeper Bosnich said.
"Especially for the second goal, you pretty much saw that again - that's why he dived backwards.
"Either he is moving just before they shoot, or more likely that his balance is a little bit too lopsided.
"Once you start diving backwards as a goalkeeper, you are in big trouble.
"He's been fantastic for Manchester United over a long period, there's no doubt about that.
"But in these last eight to 12 months there have been a consistency of errors from him that we have not seen before.
"Ole's got to seriously weigh up does he bring in Romero for these final two games. That's a huge decision he's got to make."
Bosnich believes the key will be what De Gea's frame of mind is like ahead of a crucial week in United's fight for Champions League qualification.
Defeat against Chelsea dented United's prospects of winning a trophy this season, with only the Europa League remaining, and ended their 19-game unbeaten run in all competitions in the process.
Creeping inconsistencies in De Gea's game will be a cause for concern though as they gear up for a crucial Premier League game, with implications at both ends of the table, against West Ham on Wednesday.
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"It's so important for the club to get into the Champions League," Bosnich said.
"A lot will depend on his mood and the way [De Gea] is around the training ground in the next couple of days because they can ill afford more mistakes like that going into these last two games.
"It's very difficult to, the only way to get over it is to have another game as soon as you possibly can and to play really well and to go a game mistake free."