SCOTTSDALE, Ariz. -- Infielder Emmanuel Burriss' comeback from a broken left foot was rudely interrupted Saturday when the Giants announced that he had sustained a fracture in the same area.

Manager Bruce Bochy said that Burriss will wear a walking boot for four weeks to immobilize the foot. Burriss injured himself in Wednesday's exhibition opener against Seattle as he ran out his second double of the game.

Burriss, 25, was San Francisco's Opening Day second baseman last year before being optioned to Triple-A Fresno on June 16. The switch-hitter broke the fifth metatarsal in his left foot on July 5 while running the bases and missed the rest of the season after undergoing surgery on July 10.

X-rays taken shortly after Burriss hurt himself revealed no fracture, but he subsequently underwent an MRI that revealed the extent of the injury more thoroughly. Giants foot specialist Dr. Larry Oloff informed Burriss of his diagnosis Saturday.

"It's tough news," Bochy said. "That was a long road he had coming off of the last [injury]."

Burriss had been competing for a reserve middle infield role with Kevin Frandsen. Bochy said that Ryan Rohlinger, primarily a third baseman, will be tried at shortstop to enhance the Giants' middle-infield depth.