Angels manager Mike Scioscia called it a "relief," identifying the ailment as "a little tightness on top of the forearm."
Santana was scheduled to start on Tuesday night against the Giants, an assignment that fell to right-hander Sean O'Sullivan, who was called up from Triple-A Salt Lake to make his Major League debut.
Santana, according to Scioscia, probably won't be slotted in to start until Tuesday at home against the Rockies. If he's not ready to go by then, he'll go on the 15-day disabled list, retroactive to June 12. That would have him eligible to come off the DL on June 27.
"We'll move forward for now with where he is," Scioscia said. "We have a little time. Probably not until about the 23rd [of June] is when we'll get him back out there. If he's not going to be able to make that start, we'll DL him with a back date."
Right-hander Shane Loux had a 45-pitch bullpen session on Tuesday, moving toward a return to the mound in game conditions, he said.
Loux, who is 2-3 in six starts and two relief appearances, has been on the DL since May 24, retroactive to May 17.
"I'm right on schedule," Loux said. "Once the inflammation went down, it's been fine. We'll see how I feel tomorrow, but it felt great today. Hopefully, I'll be facing hitters soon and getting back in that 75- to 90-pitch range again. It shouldn't take too long."
Loux would provide much needed rotation depth with Kelvim Escobar ticketed for the bullpen when he comes off the DL.
Lyle Spencer is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.