"I slept on it wrong," Darvish said. "If I have two or three days it will be fine."
Darvish was scheduled to throw 90 pitches Friday as he continues to prepare for the Rangers' Opening Day game against the Philadelphia Phillies on March 31.
If he makes his next start -- Darvish said he doesn't see any reason why he wouldn't -- then he would be ready to start the first game.
If the stiffness lingers, then it could put his availability in question for Opening Day.
Darvish went 13-9 with a 2.83 ERA and 277 strikeouts in 209.2 innings last season.