Arsene Wenger admits it will be "strange" to come up against Alexis Sanchez at Old Trafford on Sunday.
The Arsenal boss agreed to the Chile forward joining Manchester United in January in a straight-swap deal with Armenia international Henrikh Mkhitaryan.
Sanchez, who has described Wenger as a "football master", will face his former team-mates for the first time in what will be the Frenchman's last visit to United as Gunners boss, live on Sky Sports.
Asked if it will be a little strange coming up against the former Barcelona man, Wenger told Arsenal.com: "Of course. The only thing that has not changed is the colour, that is still red.
"It's strange for me to see him in a different shirt because he had a strong bond with the club and of course he was here for a few years. He did extremely well for us."
While Sanchez is all-but certain to start against his former employers, Mkhitaryan is struggling to be fit for the game.
A knee injury has left him on the sidelines since April 5 and, if he is close to a return, the chances are Wenger will not risk him ahead of Thursday's Europa League semi-final second leg against Atletico Madrid.
Mkhitaryan, who won the Europa League with United last season, could be key to Arsenal reaching the final after a 1-1 draw in London.
The 29-year-old has become an integral part of Wenger's plans in recent months and the Arsenal boss is pleased to have landed Mkhitaryan in exchange for Sanchez, who was running down his contract at the Emirates Stadium and would have been able to walk away for free at the end of the season..
"At the time he (Sanchez) did not accept our contract offer and the best possible way where we could get something from his departure was to make an exchange for the player of the quality of Mkhitaryan," he said.
"For him, it was a move to another big club. Overall, both parties had interest to do what happened."