Sammy Sosa was placed on the 15-day disabled list by the Baltimore Orioles on Tuesday after he failed to respond to treatment for a nagging foot injury. The move was retroactive to May 5. Sosa, who has not played since last Wednesday and missed four games, has been hindered by an abscess and staph infection on the bottom of his left foot. The right fielder has been instructed by team doctors to stay off his feet and will not accompany the Orioles on their upcoming road trip to Chicago and Kansas City. Baltimore's series against the White Sox, which begins Thursday, was to be Sosa's unofficial return to Chicago, where he played 13 seasons with the Cubs before being dealt to the Orioles in February.