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8/29/2013 1:41 A.M. ET

Chatwood may return to rotation this weekend

DENVER -- Nearly three weeks removed from competitive baseball, everything went smoothly for starter Tyler Chatwood in his Tuesday night rehab start with Triple-A Colorado Springs, putting him in prime position to rejoin the Rockies' rotation this weekend.

Chatwood allowed just one run on five hits over 5 1/3 innings, striking out four and walking two while throwing 71 pitches. He said his right elbow felt good on Wednesday, and his command improved as the game progressed.

"It had been a while, so it was awesome to get back out there and compete again," Chatwood said. "I think it was just sharpness of my command, and my command wasn't there early. They were close misses, but early on I wasn't really getting strike one. So later on I started getting ahead and felt good."

Though Rockies manager Walt Weiss didn't offer a return date for Chatwood, he said if everything checks out with the young right-hander he plans to skip Jeff Manship's start Friday and move Jorge De La Rosa and Juan Nicasio up a day. De La Rosa would pitch Friday and Nicasio Saturday, both would be on regular rest thanks to Thursday's off-day.

At 23, Chatwood (7-4, 3.15 ERA) has been one of the Rockies' best starters this year. He credits much of that improvement to developing a slider he first worked into his repertoire last year.

He was able to throw that pitch along with all his others when he took the mound for the Sky Sox Tuesday, a positive sign that he should be back in typical form when he's activated.

"I just feel like I'm an actual pitcher and being able to control the game a little better," Chatwood said. "Before, I felt like it sped up on me. Now I feel like I can slow it down when I need to."

Chatwood landed on the disabled list Aug. 7 with right elbow impingement, and Weiss will certainly welcome him back.

"He's absolutely taken that step in my eyes," Weiss said. "Not only a big league pitcher, but an impactful one I think, a guy that can really impact the rotation. He's done a great job. He's come up here and he's given us another guy that can go out there and shut down any big league lineup, and he's done it. He's pitched some really good games, particularly in our division. So he's certainly a guy to be excited about moving forward."

Fowler may return this weekend after clean MRI

DENVER -- Dexter Fowler missed his second straight start Wednesday night, but Rockies manager Walt Weiss had positive news to deliver after the game.

An MRI of Fowler's left knee revealed no tears or serious damage, Weiss said after the Rockies' 5-4 win over the Giants.

Before the game, Weiss said Fowler injured his lateral collateral ligament (LCL) when he tried to steal second in the first inning of Monday's 6-1 win over San Francisco.

Asked if the Rockies center fielder might return for the series against the Reds that begins Friday, Weiss was cautiously optimistic.

"It would probably be a stretch to see him out there on Friday," Weiss said. "But maybe at some point during the weekend."

After opening the season on a tear, Fowler's bat has cooled. He's batting .263 with 12 homers and 42 RBIs in 110 games. Charlie Blackmon started in center field and hit leadoff on Wednesday.

Rosario's primary role remains behind the plate

DENVER -- Wilin Rosario has suddenly become a semi-regular presence at first base, drawing speculation that the Rockies might plan to convert the catcher into a first baseman.

But despite his offensive gifts, manager Walt Weiss is committed to Rosario remaining the Rockies' long-term catcher. He's moved his catcher to the infield to keep Rosario's legs fresh without removing his lively bat from an order already without slugger Carlos Gonzalez.

"I envision him as a catcher," Weiss said. "But I also envision him doing this from time to time to be able to keep that bat in the middle of the lineup. So it's a nice option to have.

"As opposed to catching, it's a considerable break when you get him out from behind the plate. He wants to play, he doesn't ever want to come out of the lineup and as a catcher you're not going to play 150 or 160 games back there. So this is a way to keep him involved."

After finishing 3-for-4 with an RBI in Tuesday's loss, Rosario is hitting .317 with five homers and 19 RBIs in August. His 71 RBIs lead all big league catchers, and his 20 homers are tied for best in the Majors.

Before starting at first Aug. 11, Rosario had just one career start at first base.

The Giants have adopted a similar strategy with 2012 National League MVP Buster Posey, who has 16 starts at first base this year.

Rockies ponder September callups

DENVER -- On Sunday, Major League rosters will expand from 25 to 40 players, opening up plenty of room for players to make the jump from the Minor Leagues, and several of the Rockies' top prospects will get a chance to showcase their big league potential.

Manager Walt Weiss declined to say how many players will be called up, but he did give a slight hint as to his strategy.

"We're putting our list together, and there's still some guys I'm not sure about, we got some questions on," he said. "But it's not going to be a ton of guys. Probably some familiar faces -- guys that have been with us during the season and maybe a couple more, couple new ones."

Given Weiss' plan, shortstop Josh Rutledge and third baseman Ryan Wheeler -- who was just sent back to Triple-A Colorado Springs Tuesday -- seem likely to return. Outfielder Tyler Colvin is another likely selection after playing 27 games for the Rockies in June and July.

Relief pitchers Manuel Corpas, Mitchell Boggs and Logan Kensing, all with Colorado Springs, could also rejoin the roster.

Worth noting

• Weiss said injured outfielder Carlos Gonzalez will likely take batting practice through the end of the week before the club decides his next step. Gonzalez took batting practice before Tuesday's game for the first time since a sprained right middle finger forced him to the DL Aug. 7.

• Starting pitcher Roy Oswalt will likely throw another simulated game before he makes a rehab start or rejoins the rotation, Weiss said. Oswalt threw his second simulated game Tuesday and may toss another one Friday as he works back from a strained left hamstring.

Ian McCue is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.