The Denmark international striker, 21, was pictured leaving a London nightclub at 4am this morning with his belt undone and jeans pulled down before being helped into a waiting car.
Bendtner, who was a second-half substitute in Arsenal’s 3-1 home defeat to United, accepts it was “an error of judgement” to go out partying after such a crushing loss.
He said in a statement: “I love this club and was so disappointed to lose against Manchester United last night.
“Reaching a Champions League final is one of my biggest dreams and getting knocked out was a massive blow.
However, no matter how disappointed I was, it does not excuse my behaviour later in the evening.
“I may be young, but my actions were a poor error of judgment and something I deeply regret.
“I want to apologise to the club and the fans for letting them and myself down.
The Gunners’ hopes of reaching the Champions League final in Rome were effectively ended after just 11 minutes at Emirates Stadium, where the holders raced into a 3-0 aggregate lead with two early goals.
Manager Arsene Wenger admitted it was one the most disappointing nights of his time in charge of the Gunners, whose last trophy came back in 2005 with the FA Cup.