Hudson did not allow a run while walking two and giving up one hit against the Pittsburgh Pirates. He is 3-2 with a 2.77 ERA in eight starts this season.
X-rays were negative, but Hudson will undergo imaging tests Friday.
"Clearly there's some worry because we had to take him out of the game,'' St. Louis manager Mike Shildt said. "My hope is we were able to catch it early and take care of him.''
Hudson did not sound overly concerned.
"I just felt a little tightness in what I pretty much guess is a unique area for having something like that,'' Hudson said. "So, we decided to shut it down and make sure I'm OK.''
Hudson was replaced by left-hander Austin Gomber with St. Louis leading 1-0. The Pirates ended up winning 5-1 to snap an eight-game skid.
Information from The Associated Press was used in this report.