Jim Kelly says he's working with his nephew, Chad Kelly, nonstop to get him back on an NFL team ... and tells TMZ Sports he's confident the young QB will get another shot in the league.

25-year-old Chad Kelly was cut by the Denver Broncos in 2018 following a bizarre trespassing arrest at a random home in Colorado following a night of partying.

Jim -- his real-life uncle -- has thrown his support behind Chad and is personally helping him get his life back on track ... both on and off the field.

In fact, Jim even posted video earlier this week showing Chad working on QB passing drills.

So when we saw the Buffalo Bills Hall of Famer outside "Good Morning America" in NYC on Thursday, we asked if he REALLY thinks NFL teams will give his nephew another shot at making a roster.

"Yes, he'll have fun. He's working his tail off and I've been spending a lot of time with him," Kelly says.

"To be honest with you, he has all the materials. We'll see. God bless him, keep working and we'll see what happens."