Gerrard, who was omitted from Brendan Rodgers' starting XI, came on at the break with Liverpool trailing 1-0 after Juan Mata's goal.
But just 43 seconds after replacing Adam Lallana, the Liverpool captain was dismissed for a stamp on Ander Herrera.
No sooner had he taken the armband from Jordan Henderson, he had to hand it back as he trudged away down the tunnel.
Gerrard quickly apologised for his behaviour following the 2-1 defeat for his team.
"I need to accept it," Gerrard told Sky Sports. "I think the decision was right. I've let my team-mates and the manager down and even more importantly let all the supporters down. I take full responsibility for my actions.
"I've tried to jump his tackle and I've seen his studs and reacted wrong.
I've been in the game long enough to know that when you do something like that, especially with the timing of the game with 45 [minutes] to play and a great opportunity to get back into the game, I take full responsibility for it.
"It was probably just a reaction to the initial tackle. I don't really think I should say too much more on it.
"I've come here to apologise to everyone in the dressing room and all the supporters and players because I take full responsibility for today's result."
Sunday's match was the last time Gerrard will face Manchester United as a Liverpool player, bringing an ignominious end to his rivalry with the club.