France goalkeeper Maignan is off contract at the end of the season and talks over a new deal have stalled.
Dalmat, speaking with TMW, said his fellow Frenchman should leave Milan for a bigger stage.
He said, "For me, Maignan is the best goalkeeper in the world and deserves a lot of faith.
"Milan should do everything they can to keep him, but if I were him, I'd look around and go to another league, like Barcelona or Bayern Munich."
On the title race, Dalmat also stated: "Inter, for me, is still the most complete team, the one with the longest roster. Then I can't help but mention reigning champions Napoli.
"Finally, keep an eye on AC Milan, who will now have to focus solely on the league."