The Hall of Famer tells TMZ Sports he's friends with Jim and was devastated when he heard Kelly's oral cancer had returned.
"He's a godly man," Warner said ... "He's gonna find a way through this so I'm gonna continue to pray for him."
Kurt says he's already been in touch with the Kelly family to offer a personal message -- but encourages Jim's fans to keep up the prayers because he truly believes it helps.
Jim and his wife Jill opened up about the cancer battle earlier this week. It's Jim's 3rd bout with oral cancer but this time, he says the treatment will require a major surgery that will essentially require doctors to reconstruct his upper jaw.
Jim says he was shocked and saddened when he was diagnosed, but tells his fans, "God is with me."