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That’s according to Gunners legend and BBC pundit Ian Wright.
The Chilean finally completed his long-awaited move to Old Trafford on Monday in a deal that saw Armenian winger Henrikh Mkhitaryan move the other way.
And the 29-year-old made his debut on Friday as United comfortably dispatched League Two strugglers Yeovil 4-0 in the FA Cup fourth round.
Sanchez was lively on his first outing in the famous number seven shirt, setting up Ander Herrera for the second goal at Huish Park.
New Manchester United star Alexis Sanchez leaves the Lowry Hotel
Eamonn and James Clarke
“There was a bit of sick in my mouth at that one, to be totally honest”
Arsenal legend Ian Wright
But Wright, who spent seven years at Arsenal, admits he found it uncomfortable seeing the forward running out for Jose Mourinho’s side.
"There was a bit of sick in my mouth at that one, to be totally honest," he said.
"It's done but it's a shame to see but it's a new chapter for him.
"I don't know what to say, it's still fresh, it's still hurting."
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Sanchez lasted 72 minutes before being replaced by Jesse Lingard, who fired in the third goal late on.
Mourinho will be keen to keep his new signing fresh as he prepares to hunt down fierce rivals Manchester City at the top of the Premier League.
United are back in action on Wednesday as they travel to Wembley to face fifth-placed Tottenham.