CHICAGO -- Chicago Cubs ace Carlos Zambrano declared himself ready to return to the rotation after throwing a pain-free session in the bullpen Sunday.

 
Zambrano

Zambrano, 8-3 with a 3.13 ERA, went on the 15-day disabled list earlier this month with a right shoulder strain and likely will be activated to start July 4 in St. Louis.

He'll throw one more session on the side Tuesday in San Francisco.

"I feel great today. I guess 'Z' is back," Zambrano said, adding that he threw with no limitations. "I'm ready to go out there and do my job."

Zambrano had to leave a game against the Rays on June 18 with discomfort in the shoulder and tests revealed no structural damage. He was placed on the DL June 21, retroactive to June 19 -- just the second trip to the DL in his career for Zambrano.

The Cubs have struggled with injuries lately. Outfielders Alfonso Soriano and Reed Johnson and reliever Scott Eyre are also on the disabled list.