Mulder, who has never made a relief appearance in his career, will pitch out of the bullpen for an indeterminate amount of time. The Cardinals were down a left-handed reliever because Randy Flores is on the disabled list.
"I think we'll see how it goes," Mulder said. "I've never done this before, so let's go give it a shot."
Mulder has not pitched in the Major Leagues this season and has scarcely pitched in the big leagues since the first half of 2006. He underwent shoulder operations in September of that year and again in September '07. Mike Parisi was optioned to Triple-A Memphis to make room for Mulder on the roster.
"You might be able to get something to work in a shorter period of time than trying to stretch it out," said general manager John Mozeliak. "Just getting him back in a competitive environment and seeing where he's at makes a lot of sense for us right now."
Early this year, all indications for Mulder were positive as he tried to come back from the second operation. He threw well in Spring Training and gave the club reasons for optimism early in his Minor League rehab. But as the rehab went on, he didn't progress the way he hoped.
Mulder went back on the DL with shoulder trouble, and he began using a different arm slot. With the new delivery, he made one start on a second rehab assignment, and though the results were subpar, the reports were that he pitched well.
That led the Cardinals to hope for a start for Mulder this weekend in Kansas City, preceded by a short outing on Monday night at Memphis. But a minor back injury intervened, and Mulder did not make that appearance. He threw a bullpen session in Detroit on Thursday, with mixed results.
"I probably hoped for a little better," he said, "but it wasn't. That's kind of the way this whole process has gone."
On Friday, the decision was made to try a different tack.
"I would say it's open-ended, but my hope is that it's viewed as a step forward, and one that would be one that can grow," Mozeliak said. "And if it evolves to where he gets back in the rotation, I think that's great."
Mulder is just happy to be on a Major League roster in any capacity. He has made five big league appearances since late June '06.
"I'm definitely excited," he said. "Obviously there's a need for it, with Flo going down. I always liked facing lefties. We'll see what happens."
Matthew Leach is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.