"He'll pick up right where he left off," Romo said, according to Jon Machota of the Dallas Morning News. "I don't think it's a big challenge for Jason. The reality of it is ... if you know the game the way he does, there are certain positions - he plays one of them at tight end - he's always going to have the nuance to get open.
"Let's say he runs the exact same he always did, to me, it's just that at that position, your ability to use leverage against somebody, makes you think this and then do that. It's like the back pick in basketball. Just all of a sudden, it gets you, and you don't even know it was coming, and that guy is wide open.
"He's very intelligent with the game of football. I think he's going to pick up right from when he retired. I think you're going to see the same guy."
Romo and Witten each broke into the league with Dallas in 2003 and spent their entire careers with the Cowboys.
Witten retired after the 2017 campaign and spent last season as an analyst on Monday Night Football. His time in the booth was not well-received, but the 11-time Pro Bowler denied it played a role in his return to the NFL.