Manchester United, Real Madrid and Arsenal have all been strongly linked with a move for Mbappe, who scored 26 times last season as Monaco won Ligue 1, in addition to reaching the semi-finals of the Champions League.
Germain played alongside Mbappe at Monaco last term before leaving for Marseille, and the experienced attacker has insisted that staying with the principality club would allow the 18-year-old to "continue to play and grow".
"If he stays in Monaco, it may be the right choice because he will continue to play and grow in this club," Germain told RMC.
"After that he will probably have the chance to go to a big club, it can also be good. So it's up to him to see if he feels ready to go, but he still has a lot of talent to succeed right now in a very, very big club."
Mbappe, who recently posted an image of Monaco's new kit for the 2017-18 campaign, joined his current club from national football centre Clairefontaine in 2013.