Gregerson, who signed an $11 million, two-year contract with St. Louis over the winter, has an 8.64 ERA in 12 appearances this season. The 34-year-old right-hander recorded just one out in Tuesday's 4-1 loss at Minnesota and was charged with two runs and two hits.
"The shoulder just wasn't quite cooperating and he's got some bark in the elbow too," Cardinals manager Mike Matheny said. "So we're going to have to get a look at both. I think he's had some things periodically through a long career. He'll have them pop up, but these don't seem to be letting him do what he needs to do."
St. Louis recalled right-hander John Brebbia from Triple-A Memphis. Brebbia is 0-1 with a 2.70 ERA in six relief appearances for St. Louis this season, striking out 14 in 10 innings.
Matheny said Martinez will have another MRI this week to determine whether his right lat strain is improving. Martinez won't be ready to return this weekend when eligible and the team is considering John Gant for the open spot on Saturday in St. Louis against Philadelphia.
"Obviously he's going to miss the start here, but we're still optimistic," Matheny said of Martinez.