Please Wait . . .
The hosts were gifted an early lead at Goodison Park when De Gea's attempted clearance ricocheted off Dominic Calvert-Lewin and into the net.
Former United captain Keane was scathing in his assessment of De Gea at the interval and claims he would have been in big trouble in the dressing room if the Irishman was involved.
"Whether I was a player or a manager, I'd have killed him," Keane told Sky Sports. "What is De Gea waiting for? It's crazy.
"There's almost a bit of arrogance to him. I would have lynched him at half time. There are no excuses."
Keane also pulled no punches when it came to his analysis of De Gea's opposite number Jordan Pickford after he conceded an equaliser before half time following Bruno Fernandes' shot.
January signing Fernandes continued his bright start to his United career by firing in a low shot into the bottom corner which Pickford was unable to get to.
However, Keane suggested the England international should have done better and questioned whether Pickford is capable of playing at an elite level.
Keane added: "I don't want to hear that the ball moved. Of course it's moving, someone's kicked it!
"The bottom line with Pickford...I don't need to see the stats. I know he's not a good goalkeeper. He's not up to it."
Ex-Liverpool defender Jamie Carragher also questioned Pickford's role in United's equaliser and believes England coach Gareth Southgate will be troubled by his No.1's form.
With Southgate having a string of goalkeeping options to consider for Euro 2020, Carragher feels the England boss could have a big decision on his hands.
Carragher said: "Pickford has got to save that. He's massively at fault.
"No manager will want to move his goalkeeper this close to a tournament and Pickford has been really good for England. But it's a worry because he's been nowhere near his best this season."