Rooney, who has been appointed skipper by coach Louis van Gaal this season and is celebrating a decade at Old Trafford, was dismissed for a reckless lunge on Stewart Downing just on the hour mark on Saturday.
“I knew at the time that I misjudged it,” 28-year-old Rooney said Sunday.
“It is a red card and I don’t think it will benefit anyone to appeal against the decision. It was probably the right decision. I saw the West Ham player making a counter-attack and I tried to break-up the play, but I just misjudged it.
“I think everyone knew (I was in the wrong), so I am just grateful that the lads were able to hold on.”
His first red card at club level in five and a half years means he will likely miss United’s games against former club Everton, Chelsea and West Brom through suspension.
Rooney said he had apologised to his teammates but not Downing.
“No. I haven’t absolutely volleyed the lad,” said the England star.
“I have tried to trip him up and, to be fair to him, he got further away from me and that is why my leg is straighter than it should have been.
“As he pushed the ball away, my leg has straightened out and that is obviously why the referee has deemed it as a red card.”
Rooney, who had scored United’s opener on Saturday, will still be available to play for England in next month’s Euro 2016 qualifiers against San Marino and Estonia.
But he will not turn out for van Gaal until the first weekend of November, when United play bitter rivals Manchester City.
“That’s the most disappointing thing,” said the striker, who has scored three times for the club this season.
“I am really gutted that I am going to be missing the next three games. It is hard to take. It helps that the England games are coming up, but the training here is really good.
“It is tough and it is getting my fitness up there, so I just have to make sure I train well and be ready for when I come back.”