The Italian official gave Fletcher a straight red for fouling Cesc Fabregas in the box in United's 3-1 Champions League semi-final second leg victory.
It means he will miss the final unless the referee decides he made a mistake.
"In respect to the referee he might look at it himself without anyone asking him," said Ferguson.
"You can see the ball has moved in a different direction but we shouldn't ask him. He's competent and fair enough to look at it himself possibly. Apparently, you can't appeal and if that's the case it's disappointing for the boy.
"Darren's one of the most honest players in the game and to miss the final is a tragedy."
Uefa can rescind the red card if requested to do so by referee Rosetti, though such instances are very rare, according to BBC sports news correspondent James Pearce.
He said: "Uefa will receive the referee's report on Wednesday. In theory, he can say in the report that he made a mistake and Fletcher should not have been sent off.
"Normally that would only happen with a case of mistaken identity but Uefa says he would be able to admit the error, so Fletcher will only know for definite if he is suspended from the final when the referee submits his match report."
Arsenal manager Arsenal Wenger also insisted the red card was "very harsh" after television pictures clearly showed Fletcher played the ball cleanly.
However, it would now take an unprecedented decision by Uefa to earn Fletcher a reprieve from suspension for the final on 27 May.
The incident was the only sour note for United on the night as they outplayed the Gunners to seal a 4-1 aggregate win and book their second successive Champions League final.
United arrived at the Emirates Stadium holding only a slender 1-0 lead from last week's first leg, but United scored twice in the first 11 minutes through Park and a stunning Cristiano Ronaldo free-kick to put them firmly in control.
"We got a good start and that made the difference," said Ferguson. "The two quick goals knocked the wind out of their sails and wherever you play teams can't recover from that."
Arsenal tried to force their way back into the game but were floored by Ronaldo's second of the game after the hour.
"I thought they couldn't handle Ronaldo. That made a big difference," added Ferguson.
United now face the winner of the tie between Chelsea and Barcelona with the London club holding a slender advantage going into the second leg at Stamford Bridge after a 0-0 draw in Spain.
Ferguson though feels the hunger of his players to win the competition makes whichever team they face a moot issue.
"We should have this cup more times than we have," said Ferguson. "This is another opportunity for us to do so.
"I think we have the quality, the energy and the ambition to do it. It's a hungry team and when the chips are down they don't let me down."
and a big
to the reff.