The winger left the Gunners to join Jose Mourinho's United in the January transfer window having appeared all set to join rivals Manchester City.
It's not been plain sailing for Alexis at Old Trafford, however, with the 29-year-old often failing to replicate the high-level performances he managed for Arsenal with his new club.
Indeed, Alexis has scored just three goals in all competitions since joining the Red Devils, and has failed to find the net in his opening two appearances of the 2018-19 campaign.
He did record an assist in the 2-1 opening-day win over Leicester City although having missed the defeat to Brighton & Hove Albion, Alexis was only introduced as a second-half substitute in the 3-0 loss to Tottenham.
And Lacazette, who joined Arsenal in July 2017, appears to be enjoying the former Arsenal man's struggles, having 'liked' a post on Twitter that mocked the winger's progress for Mourinho's side.
In the image, Alexis is shown celebrating with his shirt off having scored for Arsenal, while an image of the young Marseille fan who scored after running the pitch during a ceremonial kick-off is shown alongside.
The caption reads: "Alexis at Arsenal vs Alexis at United".
The Red Devils have picked up one win from their opening three games of the season and find themselves in 13th place in the table, with Unai Emery's Gunners ninth having also claimed one win from three.