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05/26/11 4:40 AM ET

Posey hurts ankle in home-plate collision

SAN FRANCISCO -- The Giants must wait until Thursday morning before they learn the full extent of catcher Buster Posey's apparent left ankle injury.

Until then, the nightmarish sight of the team's most prized position player writhing on the ground in pain will run in a continuous loop through the minds of many Giants and their fans.

Posey, the reigning National League Rookie of the Year, was hurt during Wednesday night's 12th inning as he absorbed a home-plate collision with Florida's Scott Cousins, who scored the tiebreaking run in the Marlins' 7-6 victory. Posey received X-rays Wednesday night and will undergo a MRI on Thursday morning that's expected to reveal more about the nature of the injury.

Most Giants remained grimly silent as they dressed and left the clubhouse quickly. They would have done so under normal circumstances, having lost their second straight game and facing an afternoon series finale Thursday. But the prospect of losing Posey chilled them even more. Posey not only collaborates with San Francisco's valuable pitching staff but also bats cleanup and commands considerable respect among teammates.

Posey's ninth-inning single, which he delivered after the Giants scored four runs to erase a 6-2 deficit, increased his hitting streak to 13 games. The 24-year-old is batting .284 with four home runs and 21 RBIs.

"He's one of the leaders of the team already," right fielder Nate Schierholtz said. "What he brings every day, you can't replace."

"We're just praying it's nothing too serious," second baseman Freddy Sanchez said.

Assuming Posey goes on the disabled list, Eli Whiteside will become the Giants' No. 1 catcher. To fill the backup role, San Francisco likely would purchase the contract of Chris Stewart from Triple-A Fresno, where he was hitting .221 in 33 games. Stewart, who spent parts of the previous four seasons in the Majors with the White Sox, Rangers, Yankees and Padres, hit .321 in 20 games during Spring Training as a non-roster invitee.

The Giants might make more than one roster move Thursday morning. Infielder Mike Fontenot's strained left groin, which he sustained while running to first base in Wednesday's fourth inning, is expected to sideline him for at least a few days, and reserve outfielder/pinch-runner deluxe Darren Ford is still nursing his injured left ankle. To compensate for Posey's lost offensive impact, San Francisco could elect to promote outfielder/first baseman Brandon Belt, the organization's top prospect who opened the season in the Giants' lineup.

The fateful play occurred with one out in the top of the 12th, when Emilio Bonifacio lifted a fly ball into right field. Cousins tagged up on the play and crashed into Posey, who was trying to make the tag on a throw from Schierholtz. Posey couldn't corral the ball as Cousins bowled him over. Posey anchored himself by planting his left knee, causing him to awkwardly turn his ankle underneath him as Cousins plowed into him.

Posey remained on the ground for several minutes before being helped off the field by athletic trainers, putting no weight on his left leg. Manager Bruce Bochy, a former catcher, indicated that the sight sickened him.

"As a catcher, you know what it's like," Bochy said. "You don't like it, either, believe me. When you're trying to catch a ball, you're the only guy who players can run into. When I see him laying there, it's not a good feeling for me, or certainly not for him or his teammates or anybody."

Asked if he was surprised that Cousins tested his strong throwing arm, Schierholtz said, "I think anyone goes in that situation -- 12th inning, running out of players, 6-6. It's kind of a must-go."

Unlike Posey, Cousins emerged mostly unscathed physically. He sounded sensitive to the Giants' emotions.

"I knelt over him and tried to see if he was all right," Cousins said. "He's a great guy and a great player. I'm not trying to end anybody's season or anything like that. I am just trying to play hard. He didn't say much. You could tell he was in pain. When Bruce came out, he was pretty frustrated. I didn't want to stick around and make things any tenser. So I decided to get out of there."

Chris Haft is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.