Guerra has pitched three consecutive games and probably would be unavailable for Sunday's series finale anyway, but he said he would take his cue from the team medical staff before committing to his availability.
"It's been a little problem," said Guerra. "I've had it before. I grip the ball hard and sometimes it gets cracked."
Guerra, coming on to start the ninth inning, walked leadoff hitter Pablo Sandoval on four pitches and pitching coach Rick Honeycutt went to the mound, then explained the situation to plate umpire Scott Barry, but Guerra continued.
Manager Don Mattingly then sent Mike MacDougal to warm up, while Guerra retired Brett Pill on a fly to medium right field. Sandoval took second on defensive indifference and Brandon Belt hit a long fly ball run down by center fielder Matt Kemp on the warning track for the second out.
Orlando Cabrera singled Sandoval to third and Cabrera took second on defensive indifference before Guerra locked down save No. 18 by striking out pinch-hitter Pat Burrell.
If Guerra is unable to close games, the Dodgers would likely turn to Kenley Jansen, who struck out two in a scoreless eighth inning and has 77 strikeouts in 45 2/3 innings.
Ken Gurnick is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.