The Chilean forward is preparing for a return to familiar surroundings in fourth-round action.
United are due in north London on Friday for an eagerly-anticipated clash between two arch-rivals and Premier League top-four hopefuls.
The Red Devils will make the trip buoyed by a run of seven successive victories under Ole Gunnar Solskjaer.
Sanchez has played little part in that record-breaking sequence after nursing a series of niggling knocks, but is ready to step back into the fold and ignite his United career against a former club.
Ex-Arsenal defender Keown told the Daily Mail of the threat posed by a man who has endured a difficult time since moving to Old Trafford in January 2018: “Ole Gunnar Solskjaer has been waiting for the perfect moment to re-introduce Alexis Sanchez.
“What better opportunity for the forward to relaunch his Manchester United career than by going back to his old club and knocking them out of the FA Cup?
“Not only will he be desperate to prove a point to the Arsenal fans, but Sanchez gets a real buzz from playing in this competition.
“He has scored in two FA Cup final victories with Arsenal and found the net in three semi-finals — including for United against Tottenham last season.
“He could cause Arsenal serious problems down their left flank. Sead Kolasinac plays as more of a wing-back than a defender, often leaving gaping holes behind him.
“Those are the kind of spaces Sanchez will be looking to exploit to destroy Arsenal’s FA Cup dream. This is a player who needs the love of his manager.
“Solskjaer has been talking him up in recent weeks as if readying him for this huge clash at the Emirates.”
Sanchez will not be the only attacking star on show at Emirates Stadium, with Keown expecting an entertaining encounter between two sides full of confidence.
He added: “Friday night will be a stern examination of both sets of defenders. Alexandre Lacazette and Pierre-Emerick Aubameyang are as good as any strike partnership in the Premier League.
“United can threaten Arsenal’s centre-backs with their pace, too. Sokratis is quicker than he is given credit for, but has a habit of getting the wrong side of his opponent and fishing for the ball.
“Both sides have kept just four clean sheets in their 23 Premier League games, so this could well be a high-scoring game.
“I’m hoping for a thrilling contest that ends 3-2... and I believe Arsenal’s firepower will be enough to inflict a first defeat on Solskjaer.”