DENVER -- Currently in the Minor Leagues on a rehab assignment, Mark Mulder was diagnosed with a mild rotator cuff strain of his left shoulder on Wednesday morning. The Cardinals left-hander had been scheduled to pitch again Saturday against Triple-A Tucson, but he is now set to rest for the next week to 10 days before a re-evaluation.

After experiencing shoulder fatigue following his rehab start in Triple-A Memphis on Monday, Mulder returned to St. Louis for a follow-up visit with team physician Dr. George Paletta, who performed shoulder surgery on Mulder in both September of 2006 and 2007.

"I think it's just Mother Nature saying slow down some," manager Tony La Russa said Wednesday. "He should get all [the time] that he needs. We don't need him to get here. We need him to get here and pitch like he can. He should get all the time he needs to make that."

Mulder has made five rehab starts in the Minor Leagues, and his rehab assignment is scheduled to end on May 14. He has posted a 6.66 ERA over his five starts, including a 13.03 ERA in two Triple-A games.

The Cardinals' pitching staff, meanwhile, is holding its own without the veteran left-hander, leading the league with 22 wins and trailing only Atlanta and Arizona with a 3.59 team ERA through Tuesday.

"That's just the point," La Russa explained. "Suppose we were struggling. You can't put it on Mark Mulder. It's like last year, that's what he tried to do. We tried to tell him the exact opposite, but he's a good teammate and he tried to push, push, push [to return from the disabled list quickly], and look what happened, he re-injured himself."

After missing the first 135 games of the season, Mulder made four Minor League rehab starts in 2007 and then returned for three Major League games in September before it was determined that he needed arthroscopic surgery.

"It really doesn't make any difference for him what's happening on the pitching staff," La Russa reiterated. "This guy's a premiere guy and he ought to have all the time he needs to get right. He's been out a long time. Hopefully it's a slight strain or something, a little shoulder fatigue. Back him off and he'll be better for it."