The Chilean has opened a new chapter in his career after taking the decision to leave the Gunners for Old Trafford, with his Red Devils bow made in an FA Cup win over Yeovil on Friday.
Parlour is among those disappointed to have seen a top talent slip the next at Emirates Stadium, however thinks the 29-year-old's quality could prove influential in Jose Mourinho’s quest to return European football’s biggest prize to Manchester.
He explained to Sky Sports what Sanchez will add to the United fold: "Sometimes they have to drag him off the training field. He’s always out there, he don’t want to miss a game.
“I think his energy will come through with the other players as well and his goals, he will score you plenty of goals.
“You can’t always rely on [Romelu] Lukaku, if he has a bad spell you’ve got players behind him now to score goals.
“He’s going to be a lot more prolific probably than the players in around him. Champions League football as well, he can play straight away.
“He could be brilliant this season. That’s probably why he wanted to get the deal through quickly because he’s another asset for them in the Champions League.
“That could be the difference in getting them to the semi-final or final.”
They have important domestic outings to come before then, though, with Mourinho’s men set to take in meetings with Tottenham, Huddersfield and Newcastle before attention turns to continental competition.
Priceless points will be up for grabs in those fixtures, with the Red Devils currently sat second in the Premier League table, 12 points behind leaders Manchester City and only three ahead of third-placed Chelsea.