Ethier and his 29-game hitting streak were scratched from the Dodgers lineup 40 minutes before Wednesday's 5-1 loss to the Cubs. He will be examined by team doctor Neal ElAttrache in New York on Thursday.
Ethier said he suffered the injury April 16 on a slide into home against the Cardinals, meaning he's had it through the last 16 games of his streak. He said it is more tender throwing than swinging.
"It was on a slide against St. Louis at home, a close play, I think it was [James] Loney hit a ball to [Albert] Pujols and I slid around [the catcher] and hyperextended or jammed the elbow reaching for home plate," he said. "I've felt it on and off the last couple weeks.
"If it's nothing serious, just a sore elbow or bone bruise, I'll deal with it."
Mattingly said the first he heard of the injury was after Tuesday night's game. After Ethier told him he was "good to go," Mattingly put him in Wednesday's lineup, but scratched him 40 minutes before first pitch when Ethier told him he couldn't get loose after throwing in the indoor batting cage.
"You can't let him go out there and do damage to himself and he'd need more time," said Mattingly. "I had to bite the bullet with him, give him a game or two and hopefully he'll be ready Friday."
Ethier said the timing of Thursday's travel day to New York for a series that starts Friday night came into play.
"I've got back-to-back days to rest and let it calm down," he said. "It's sore to bend and straighten out."
Mattingly said he wouldn't hesitate using Ethier to pinch-hit if a logical situation arose.
"We have to," he said. "We're trying to win a game. I'd like to protect him any way I can to keep this going, but if the game's on the line and it's a spot for him, I don't think he'd say, 'Don't hit me here so I can extend the streak.'"
Ken Gurnick is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.