The Red Devils were held to a disappointing 1-1 draw with promoted side Wolverhampton Wanderers at Old Trafford.
Summer signing Fred broke the deadlock in the first half before Joao Moutinho equalised in the second half.
Manchester United were 3-0 winners against Young Boys in the Champions League in Switzerland on Wednesday night.
The 20-time English champions are in seventh place and eight points behind current Premier League leaders Liverpool FC.
Former Spurs forward Crooks heaped praise on De Gea for his outstanding performance at Old Trafford.
“He’s only gone and saved United again for the third consecutive week,” Crooks told BBC Sport.
“He did it against Burnley, then Watford and now Wolves. David de Gea is in magnificent form – the save from Raul Jimenez with his legs was as instinctive as it was brilliant.”
Manchester United won three successive games in all competitions before a 1-1 draw with Wolves in their sixth Premier League fixture of the season.
The Red Devils impressed in Switzerland thanks to goals from Paul Pogba and Anthony Martial to make a perfect start in Switzerland.
Crooks believes Mourinho can have little complaints after Wolves’ impressive performance.
He added: “However, it was the stop from Willy Boly’s header that kept United in the game.
“United boss Jose Mourinho can moan all he wants about a lack of motivation from his team, but when you’ve won in the Champions League in midweek and gained a valuable point in the following fixture having not played well, you count your blessings.”
Manchester United finished in second place in the Premier League table last term to secure their best finish since Sir Alex Ferguson.
The Red Devils haven’t won the Premier League title since 2013.
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