Candidates to replace Mientkiewicz are Blake DeWitt, who was sent to Triple-A Albuquerque Monday, and rookie Xavier Paul, who is batting .571 at Albuquerque. A decision will be made Friday.
Both DeWitt and Paul bat left-handed, as does Mientkiewicz. Delwyn Young would have been the likely replacement, but he was traded Monday night to the Pittsburgh Pirates for two players to be named.
Mientkiewicz suffered the injury in the sixth inning with an awkward head-first dive -- and an unnecessary one -- as there was no play on him. He reached forward to break his fall and his right arm appeared to be pushed sideways when his right palm hit the dirt.
"I slid way too early and as soon as my hand hit the ground, I felt and heard a crunch and it popped out," said Mientkiewicz, his arm in a sling and an MRI scheduled for Friday.
Down for a moment in pain, Mientkiewicz successfully argued to stay in the game, but two batters later he came off the field in obvious pain with his arm dangling.
"They popped it back in and it felt fine, actually, but I tested it by pushing down on my helmet and it popped back out again. I feel like I let [manager] Joe [Torre] down and I let my guys down.
"I'm just crushed. It's like every time I play for Joe, something stupid happens. Every time I get a dream job, something happens."
He said while playing for Torre in New York, he suffered a broken wrist, a concussion and a sprained neck. "The diagnosis doesn't sound real pleasant. I'm devastated right now. Joe and everybody stuck their neck out for me and this is what I give back."
Although Mientkiewicz could have gone in standing up, he said he saw Giants shortstop Edgar Renteria out of the corner of his eye "thought he was reaching for the ball."
Mientkiewicz made the club as a late-arriving non-roster invitee to Spring Training and effectively took the job that Young held last year. Mientkiewicz was 2-for-5, with both hits being pinch-hits.
Ken Gurnick is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.