SAN FRANCISCO -- Rockies right-hander Aaron Cook was rusty but pain-free in a simulated game Tuesday afternoon at AT&T Park. Three other Rockies pitchers also participated in the session.

Fellow righty Jose Contreras also threw in the same simulated game. But Cook, who has been out since leaving an Aug. 21 start because of right shoulder soreness, might be closer to returning than Contreras, who suffered a right quadriceps strain in his last start. Contreras' mobility is still limited.

Jeff Francis, who hasn't pitched since undergoing left shoulder surgery in February, also threw in the simulated action. It was his first time facing hitters this year. Right-hander Huston Street, who has missed recent action with a right biceps strain, played catch and finished throwing from the slope of the mound.

Cook (10-6, 4.47 ERA) said he was more concerned about health than sharpness, so he deemed the simulated game a success. He's planning on another simulated game Saturday.

"There's a little rust on there, but there's no pain," Cook said. "That's pretty much what we were going for today. There's nothing in there grabbing still."

Manager Jim Tracy said his plan is to send Cook to the Rockies' instructional program in Tucson, Ariz., if he checks out fine after Saturday's simulated game. He would like for Cook to throw in a regular-season game before considering him for the postseason should the Rockies qualify.

"I am optimistic," Tracy said. "I think it's of utmost importance. Because of the amount of time he's been down, to grab hold of him and just throw him into a gut-wrenching situation, you're doing a disservice to the player. I won't do that."

A possible return date could be Sept. 25, but Cook said he's trying not to look at the future. Tracy said the ideal procedure would be for the Rockies to lock up a playoff spot, then have Cook pitch in a low-pressure game before the regular season is done.

Contreras isn't a candidate to return until he regains mobility for fielding and covering bases.

"He had no problem pitching, but he still can't run," Rockies head athletic trainer Keith Dugger said. "We're just trying to keep his arm in shape."

Contreras is 1-0 with a 1.86 ERA in two starts with the Rockies, who acquired him in a trade with the White Sox. Contreras was 5-13 with a 5.42 ERA in 21 starts with the White Sox.

Street, who converted all but one of his 34 save chances before the injury, will have a "touch-and-feel" bullpen session Wednesday, should he not experience soreness after Tuesday's throwing session, Dugger said. Left-hander Franklin Morales is 6-for-6 on save chances and 0-1 since Street's injury.

The plan is for Francis, who threw all of his pitches Tuesday, to be ready to pitch in the fall instructional program as part of a program that the Rockies hope will have him ready for 2010.