In the fifth inning, Sanchez, a three-time All-Star, stopped a ground ball hit up the middle by Brandon Phillips. Sanchez braced himself by using his right hand while sliding on the edge of the outfield grass and was slow to get to his feet, while in obvious discomfort.
San Francisco Trainer Dave Groeschner said prior to Sunday's game against Cincinnati that Sanchez, who underwent surgery on his left shoulder in December, suffered damage to the labrum. Sanchez reportedly underwent an MRI Saturday.
The Giants said Sanchez will be examined soon by Dr. Gary Waslewski, who performed surgery on Sanchez's left shoulder, in Arizona. The Giants said their plan will be to check how Sanchez's shoulder responds to several weeks of rehab before deciding their next move.
"We'd like to avoid [surgery], but at this point we'll have to see," Groeschner told mlb.com. "We have to make sure he's good for next year, too."
To replace Sanchez, 33, the Giants signed veteran utility man Bill Hall as a free agent.
Several Giants, including relief pitcher Sergio Romo, said Sanchez will be difficult to replace.
"It's never good to lose a player of the caliber of Freddy Sanchez," Romo told mlb.com. "You can't replace him. He's been the most consistent guy on our team on both sides of the ball."
Sanchez, who was acquired from the Pittsburgh Pirates in 2009, is batting a team-best .289 (69 for 239) with three home runs and 24 runs batted in. In 60 games, Sanchez has 15 doubles and has scored 21 runs.
The Giants enter today's road game against the Arizona Diamondbacks at 37-29 and in first place in the National League's West Division.
The Giants have had 12 players on the disabled list this season, including star catcher Buster Posey for the rest of the season because of a leg and ankle injury. Last season, they had 13 players make trips to the disabled list before winning the franchise's first championship since 1954, when it resided in New York.