The extent of the injury is still unknown. The team will wait until Weaver undergoes an X-ray and MRI on Tuesday before deciding whether he'll need to go on the disabled list.
"I really don't have any answers right now," Weaver said. "I've just got to wait for those MRIs and X-rays to come back. We'll keep our fingers crossed."
So will the rest of this team, which extended its season-high winning streak to seven games and can ill afford to lose its best starting pitcher. If Weaver does go on the shelf, the Angels could call up young righty Garrett Richards from Triple-A Salt Lake (though he has a 6.30 ERA in May) or perhaps get in on veteran free agent Roy Oswalt (but that would depend on his price tag).
The Angels will "most likely" be calling up a pitcher on Tuesday regardless, manager Mike Scioscia said, considering the bullpen just accounted for nine innings and the club hasn't had a day off since May 10.
But as of late Monday night, they were keeping their options open with Weaver, who could be helped by a Thursday off-day.
"We won't know that far yet," said Weaver, who felt the pain on the lower part of his right side. "I'll wait for the results tomorrow and go from there."
Weaver has never really dealt with back pain much, but his good friend, Dan Haren, has. Haren has been dealing with some stiffness in his back throughout the year, but he doesn't have as much torque in his delivery as Weaver -- and an MRI could reveal a bulging disk for Weaver.
"I can't really bend over too much," Weaver said. "Muscle relaxer's helping a little bit, but like I said, I've never had something like that happen before, so it was pretty painful. No doubt about it."
Weaver, who's 6-1 with a 2.61 ERA in a year that has seen him throw a no-hitter, didn't have any pain coming out of the bullpen for his start. But on his 12th pitch of the game, a 1-0 fastball to Yankees cleanup hitter Robinson Cano, he felt a pronounced pinch in his lower back.
"It felt like somebody came up behind me and stabbed me," Weaver said. "I couldn't bend over."
Weaver was checked on by Angels trainers and could barely throw a warm-up pitch, then came right out of the game, hobbling back to the dugout and making way for Bobby Cassevah to come out of the bullpen.
"Very disappointing," Weaver said. "You get motivated for games like this and to have that happen so early in the game, it's just disappointing."