Terrell Davis is issuing a stern warning to Saquon Barkley ... saying if the injured running back returns too early from his ACL injury, it could have DIRE consequences.
The Hall of Famer explained it all to TMZ Sports ... with Davis telling us when he rushed back early from a knee injury following the 1999 season -- and it cost him A LOT.
"For me, I tell players coming back from an injury is sometimes you have to protect yourself from yourself," Davis says. "And, what I mean by that is we're very competitive and we want to come back and beat the timeframe.