Gay football players NEED to have thick skin ... 'cause there's a 100% chance they'll get "teased" in an NFL locker room if they come out ... so says NFL legend Barry Sanders.

The Detroit Lions icon had just touched down in New Orleans last night when we asked him if gay players pose a "problem" in NFL locker rooms.

Sanders response -- absolutely not -- adding, "I don't know that there haven't been MANY gay players [in the past]."

Sanders said gay players should not be afraid to come out to their teams -- but need to know that they WILL be teased in the locker rooms afterward ... because "in a locker room you get teased for anything."

He adds, "If somebody comes out, they're gonna get teased, but they need to have thick skin and go on about their life."