UPDATE: Posey’s MRI showed a bone bruise and ruled out ligament damage. He is day to day.

SAN DIEGO – Buster Posey is out of Monday’s lineup at Petco Park and the Giants were awaiting MRI results on his ailing left thumb.

Posey went for the precautionary tests Monday because the injury got worse over the weekend at Arizona, when he went 1 for 11 and hit one ball out of the infield. He has dealt with discomfort ever since Aug. 20, when his thumb was bent back while applying a tag on a play at the plate against the Phillies.

Posey said he anticipated needing two or three games to let the thumb calm down, which means he might miss the entirety of this series against the San Diego Padres.

“It just hasn’t felt great,” Posey said. “Yeah, I could play. I mean, I played for a week. I’d like it to calm down to where I can take an aggressive swing.”

Giants manager Bruce Bochy was hesitant to call Posey anything beyond day to day until the club can evaluate the MRI results. The tests were precautionary to ensure there were no torn ligaments, Bochy said.

“It’s bothering him quite a bit,” Bochy said. “He wasn’t really talking about it, but it was affecting his swing.”

Posey was available in an emergency, with Kelby Tomlinson next on the catching depth chart. Of course, Pablo Sandoval arrived in the big leagues as a catcher, too.

The Giants should have a true backup when rosters expand on Friday. They’re expected to purchase the contract of Tim Federowicz.

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Hector Sanchez, who has hit four of his eight homers this season against his former team, is in the Padres lineup. What, you thought they’d bench him?

Sanchez is 4 for 6 with a double and two homers against Jeff Samardzija, who gets another crack at him.

Lineups: