Theismann, now an NFL Network analyst, explained his frustrations with the quarterback on NFL.com's "Dave Dameshek Football Program", calling Romo "average" and saying the Dallas Cowboys need to actively seek a replacement.
"Tony Romo continues to do things to hurt his football team," Theismann said on the podcast, which was released Thursday. "He doesn't understand how to play the quarterback position. Somebody had to say it, and I just said it. Tony, you have to start proving to everyone you understand football. You're doing things that Pop Warner kids would get benched for."
Romo has been a frequent target of NFL analysts this season, with criticisms peaking after he threw three second-half interceptions to allow the Detroit Lions to rally for a 34-30 victory last week. Former Cowboys cornerback Deion Sanders, also an NFL Network analyst, said Romo isn't the right quarterback in Dallas.
Theismann echoed that sentiment, saying the Cowboys need to start looking for someone other than Romo and 39-year-old backup Jon Kitna to guide the offense.
"I think the Cowboys seriously have to start looking to the future," Theismann said. "We've seen Romo do a lot of different things, and he was very courageous with the ribs (which were broken in Week 2), but this game was unforgivable, at this level or even on a college level."
Theismann also took aim at New York Jets quarterback Mark Sanchez, calling him a "middle-of-the-road guy," but he was effusive in his praise for Green Bay Packers signal-caller Aaron Rodgers, whom he called "the best pure passer in the history of football."
"We've never seen all of the elements that go into the greatness of throwing the football in one individual like you see in Aaron Rodgers," Theismann said. "And he's got a cockiness about him that I absolutely love. When you walk out there, you have to think you're the baddest man in the valley. Aaron Rodgers does that, and the team believes in him."