Fletcher had a superb game as United demolished Arsenal 3-1 in the second leg of their semi-final at the Emirates Stadium, but was sent off by Italian referee Roberto Rosetti for a 75th-minute challenge on Cesc Fabregas.
UEFA spokesman Rob Faulkner told Reuters on Wednesday while United had the right to protest the decision, there was nothing in UEFA's rules that would allow Fletcher to escape the ban.
Faulkner said: "Manchester United have the right to protest the decision within 24 hours of the match.
"However the protest is only admissible if the referee made an error and mistakenly identified and cautioned or sent off the wrong player.
"There cannot be an appeal against a factual decision taken by the referee, and there is nothing to indicate that the referee made a mistake in identifying Fletcher as the player he penalised last night."
Even if Rosetti was to admit his decision was wrong, the red card would still stand under article 44.4 of UEFA's disciplinary regulations, which only allows red cards to be rescinded for cases of mistaken identity.
Television replays showed the 25-year-old Scottish international, had his eyes focused on the ball, which he played before colliding with Arsenal skipper Fabregas.
Rosetti, however, judged Fletcher had denied Fabregas a goal-scoring opportunity and that he had no alternative but to award Arsenal a penalty and send the Manchester United man off.
Fletcher was an unused substitute when Manchester United beat Chelsea in last year's final in Moscow but manager Alex Ferguson said after Tuesday's match he would probably have featured in the final in Rome on May 27.
"You can see from his performance tonight, he's been a key player for us in all of our big games this season. I couldn't tell you whether he would have definitely played in the final but you would have thought that Darren would have figured largely."
GLORIOUS NIGHT
Ferguson said he had not spoken to the referee after the match.
"He may look at himself without anyone asking, but I don't think we should ask him. He's competent and fair enough to look at it himself.
"Apparently we cannot appeal and if that's the case that's really disappointing."
Fletcher's sending off aside, United enjoyed a glorious night at the Emirates, sweeping into a 2-0 lead with goals from Park Ji-sung and Cristiano Ronaldo after 11 minutes to all-but kill off Arsenal, who at that stage were trailing 3-0 on aggregate.
They made it 3-0 with a sweeping counter-attacking goal converted by Ronaldo midway through the second half and while Robin Van Persie converted the penalty after Fletcher's dismissal to make it 3-1, the night belonged to United.
The Manchester side now have the chance to become the first club since the Champions League started in 1992-93 to retain the title.
