"He'll probably be out four or five weeks," Cubs general manager Jim Hendry said Friday. "It will be three weeks before he can throw."
Gryzlo looked at the MRI taken on Mateo's forearm and elbow before coming up with his determination.
"He has an injury that is almost identical but not quite the same severity of Randy Wells'," Hendry said, in comparing it to Wells' injury that kept him out seven weeks. "There's no ligament damage in the elbow. It's slightly less the degree of Randy's but very similar."
Hendry said Mateo will go to Mesa, Ariz., where the team's training headquarters are located. He had previously thrown 57 pitches on May 30 in long relief of starter Carlos Zambrano, who left that game in the second inning with lower back soreness. Zambrano has since been put on the DL.
"He went 57 pitches," Hendry said. "He's thrown in the 40s before. What are you going to do? He threw a side session two days later and he was pain-free. He was probably hoping he'd be a starter. I don't look at [the injury] like that."
The Cubs put Mateo on the DL Tuesday. He left Monday's game after throwing just pitches. He has a 4.30 ERA in 23 appearances this season.
Bruce Levine covers the Cubs for ESPNChicago.com.