Jhoulys Chacin thinks something is wrong with his right arm. He's not sure what, but throwing 86 mph fastballs tells him something is not right.

"I really don't know what's wrong with my arm. I can't get strong," the right-hander said in a whisper in the quiet Rockies clubhouse after a 7-4 loss to the Brewers on Saturday. "Even if I throw extra hard, I can get one (pitch), but then I can't throw the next one hard."

The Rockies' rotation has already been decimated by injuries, meaning the club desperately needs better from Chacin. But after 11 starts, he's 1-7 with a 5.40 ERA. He was gone after 5 innings Saturday, having given up seven runs on 11 hits.

"This was similar to some of his previous starts," manager Walt Weiss said. "The pattern has been it takes him some time to settle in. He says he doesn't have any pain, but he struggles to get loose."

Chacin missed spring training and spent a month on the disabled list at the beginning of spring training because of a shoulder strain.

Anderson update. Lefty starter Brett Anderson is itching to pitch.

He will throw one more batting practice session Sunday before heading to Triple-A Colorado Springs for his first rehab start Wednesday. He's been on the disabled list since April 13 with a fractured index finger on his throwing hand.