All-Star second baseman Freddy Sanchez, who dislocated his shoulder on June 10, will undergo season-ending surgery on Tuesday, while starting pitcher Barry Zito is returning to the disabled list because of a nagging right foot sprain.

Sanchez, a .289 hitter this season and an infield mainstay, had been working his way back to full fitness in the hope of returning to the line-up but was unable to restore comfort in his throwing shoulder.

"We were still optimistic that he could find a way to rehab and get to a point where he could help us," Giants manager Bruce Bochy told the team website (sanfrancisco.giants.mlb.com).

"But as each day went by, we knew his chances were diminishing. It's at a point where we have to make a decision to make sure he's ready for next year."

Zito was sidelined earlier this season with his foot injury, but came off the DL on June 28 and strung together a few solid starts before losing form.

Compiling a modest 3-4 record and a 5.62 ERA this season, the left-hander has allowed 19 runs in 15 2/3 innings over his last three starts, walking eight batters.

National League West division-leading San Francisco (61-48) will activate left-hander Jonathan Sanchez to fill the void left by Zito, who has not been given a return date.

(Writing by Jahmal Corner in Los Angeles; Editing by John O'Brien)