BRADENTON, Fla. — The Pittsburgh Pirates purchased infielder Luis Rivas' contract from Triple-A Indianapolis on Tuesday and will start him at second base on opening day if Freddy Sanchez's sore shoulder isn't better.

Right now, Sanchez's shoulder isn't improving, and it's becoming a bigger worry to the Pirates as the season draws closer and he still can't play defensively.

Sanchez, an NL All-Star the last two seasons, has played only twice in the field this spring because of recurring right shoulder pain. He has been diagnosed with tendinitis, but the Pirates remain hopeful he can play in their opener Monday in Atlanta.

Sanchez didn't sound optimistic Tuesday about being game-ready in less than a week, saying he doesn't want to go through the season repeatedly taking cortisone shots just to play. He had arthroscopic surgery late last season to repair a shoulder problem not related to this one.

"When I hit, it's fine. When I run, it's fine. Even when I throw lightly, it's fine. It's not until I throw hard, I try to let it go, that it doesn't cooperate," Sanchez said. "That's why I'd rather take more time off now, than go through the whole season like this because this is not fun."

In addition to promoting Rivas, the Pirates cut four players, including former Yankees outfielder Kevin Thompson, and are down to 33 in camp, eight over the limit.

Thompson was optioned to Triple-A, while non-roster left-hander Casey Fossum and right-hander Elmer Dessens were reassigned to the minor league camp. Right-hander Jonah Bayliss was designated for assignment, creating a spot on the 40-man roster for Rivas.

Rivas, the Twins' starting second baseman for most of the 2001 through 2004 seasons, has a .348 average with no home runs, five doubles, a triple and three RBI this spring. He has played only four games in the majors since the 2005 season, all with Cleveland last season.

"Luis has done the job all spring, with the bat and the glove," said general manager Neal Huntington, who saw Rivas extensively while working previously in Cleveland's front office.

In other moves, Atlanta traded relief pitcher Tyler Yates to the Pirates today for minor league pitcher Todd Redmond.

The 22-year-old Redmond is 22-21 in three minor league seasons.

Yates, a 30-year-old right-hander, appeared in 131 games in relief during the last two seasons. He is 6-12 in his career with a 5.15 ERA.