The Yankees activated right fielder Gary Sheffield from the 15-day day disabled list on Tuesday, and closer Mariano Rivera threw a bullpen session and said he hopes to return this weekend. Sheffield, who had wrist surgery June 13, did not start against Toronto on Tuesday night. Manager Joe Torre said he will start playing first base after the Yankees clinch the AL East title. Their magic number was three entering Tuesday's play. "Once that happens, he'll probably get a lot of work," Torre said.