Pepe, 23, has had a superb season, scoring 21 goals and grabbing 12 assists for the Ligue 1 runners-up.
Galtier told Canal+: "Nicolas Pepe will leave. Life's like that, football's like that today.
"He is a player of the highest level who will have a big decision to make on the choice of his next club.
"There will be a battle between the great European teams.
"I hope that he will take good amount of time to think about it, do his research, like he did when he came here and when he decided to stay here [last summer], find the right project."