After the big Belgian's late goal, Mourinho kicked over a case of water bottles and picked up another, firing it back to the ground.
The Red Devils managed to secure their spot in the last 16 of the Champions League on Tuesday night thanks to Marouane Fellaini's last minute victor in their 1-0 victory over Young Boys at Old Trafford.
But for much of the game, it didn't look like that victor was going to come for the Red Devils and, as we so often see, United finished the match by pumping balls up towards Fellaini as they desperately searched for a goal.
The United goalkeeper made a stunning save from Young Boys' Michel Aebischer when the score was still 0-0.
The Belgium global was benched for clashes with Everton and Manchester City, playing a total of 58 minutes across the two games, while he was also a substitute against Young Boys in the Champions League on Tuesday. As he turned, he appeared to control the ball partly with his hand, before hitting a shot through Loris Benito's legs and into the bottom corner.
Mourinho, who shares agent Jorge Mendes with De Gea, has backed the player to sign a new contract.
"It reminded me very much of the Seville game past year".
"Without David's save, no winning goal either", he said (via the Guardian).
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Following a 0-0 home draw against Crystal Palace at the weekend, United will hope they can turn in a better display on the road when they travel to face Southampton on Saturday in Premier League play. "I became better, I improved as a player".
"Of course I'm happy with the way we started - the intention that we started with was exactly that intention".
The long road to recovery was a hard one, and even since his return to fitness, he has been subjected to a lot of harsh criticism from his own manager, José Mourinho.
We could see Fred far more involved in the United first-team over the Christmas period.
"We've just scored a goal but we're talking about Jose Mourinho's reaction", Ferdinand added in the studio.
"So I'm pretty sure that a proper football manager would never criticise another one for emotional reactions on the touchline because it's deja vu for them".
The home side's best effort came in the opening minutes of the match when Marcus Rashford's chip from Jesse Lingard's through ball was sent over the bar.