Buchholz had a career year with a 2.17 ERA in 63 appearances in 2008 but suffered an elbow injury during Spring Training 2009. He was 0-1 with a 7.94 ERA in five appearances for Triple-A Colorado Springs, after one scoreless appearance at Class A Modesto.
"He had back-to-back outings, and after the second one was beginning to complain about stiffness in his lower back, so they brought him in and took him off his rehab assignment," Rockies manager Jim Tracy said Friday.
The news was a little better for reliever Franklin Morales, who had an up-and-down stint as closer before left shoulder stiffness forced him to the disabled list on May 20. Morales struck out two and gave up one hit on Thursday, with no walks an one hit batter, in two scoreless innings in Colorado Springs' 3-2 loss to Omaha.
"The reports I got were all very good," Tracy said. "His velocity was up where you'd want it to be. Obviously from telling you he walked nobody, his command, with the exception of the hit batsman, was for the most part, very solid."