The Spain international has been one of Manchester United’s most consistent players in the 2017-18 Premier League season.
De Gea helped Manchester United to finish in second place in the Premier League table ahead of Tottenham Hotspur, Liverpool FC and Chelsea FC.
The 27-year-old has been regularly linked with a move to La Liga giants Real Madrid over the past couple of summer transfer windows.
Los Blancos were linked with the a swoop to sign the former Atletico Madrid shot stopper last summer but Mourinho managed to keep hold of his number one goalkeeper.
De Gea is widely recognised as the Premier League’s best goalkeeper but the Spain international has only managed to win one Premier League title.
Former Spurs forward Crooks has challenged Manchester United to improve their defence to give De Gea more support in goal.
“The moment Jose Mourinho persuaded David de Gea to stay at Manchester United, rather than leave for Real Madrid, you knew something was brewing,” Crooks told BBC Sport.
“Neither have managed to win the title this season, but I wouldn’t bet against them next term.
“De Gea has once again looked imperious in goal, and one player in the United set-up who warrants the accolade ‘world class’. The issue for Mourinho is he has not been in a position to assemble a defence worthy of his keeper.
“Petr Cech had William Gallas, John Terry and Ricardo Carvalho to protect him when Mourinho was manager at Chelsea in 2004-05. That’s why they won the title and why United haven’t.”
Manchester United will take on Chelsea FC in the FA Cup final at Wembley next weekend.
The Red Devils signed Chile international Alexis Sanchez in a swap deal from Arsenal in the January transfer window.
Manchester United signed De Gea in a £17m deal from Atletico Madrid in 2011.
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