"He needs a couple weeks without throwing," manager Bruce Bochy said after Thursday's 11-6 loss to the Rockies in the rubber game at Coors Field. "He's going to be down for awhile. I can't tell you how long."
Head athletic trainer Dave Groeschner confirmed the timetable, noting that they'll evaluate Romo after the initial two-week period of inactivity.
Romo left the team before Thursday's game to return to San Francisco for tests on his elbow. He had been fine on Tuesday, but started to feel discomfort in the elbow when playing catch before Wednesday's game against the Rockies.
This is the same injury that cost Matt Cain 94 games on the DL during the 2015 campaign, but Romo's return won't necessarily take as long.
"I guess it depends on how bad it is," Cain said. "For me, it was three weeks to let the flexor heal, so no throwing. And I had to start back over to throw and find ways to get your pitch count back up. It's almost like a whole offseason again, because I was getting the pitch count back to 100 where it needed to be.
"Being a starter it's definitely different. Let's hope that his is not nearly as long of a timetable as mine was."
The situation makes the Giants' decision to start the season with 13 pitchers, including eight in the bullpen, seem prescient.
"Right now, we need 13 men," Bochy said, noting the Giants have only one off-day in the first 23 games of the season. "Once we start getting a few more days off, we could change. It's worked out fine. I haven't been short on the bench. Really, the only guy I'm going to pinch-hit for is the pitcher. Or a double switch. I don't see us changing back to 12 [soon]. We could be like this for a while."
Owen Perkins is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.