Former United forward Depay will return to Manchester on Wednesday, French visitors Lyon facing Premier League holders City in their European opener at the Etihad Stadium.
Depay found himself on the outer under Van Gaal before Jose Mourinho arrived and granted the Dutchman a move to Ligue 1 in 2017.
“Certain things that happened I don’t want to say now in public.
“I still speak with lads from United and I wish everybody the best. Manchester is still red!’
Responding to Rooney’s comments, Depay said: “Some people can’t take a joke and me and Wayne are very good friends.
“I don’t have a red leather jacket out of my thousand leather jackets! I understand what he meant with it and that’s it.