NEW YORK -- Worried about Chuck Knoblauch's sore right elbow, the New York Yankees brought their former backup infielder, Luis Sojo, back from the Pittsburgh Pirates in a trade for a minor league pitcher Monday.

The trade was completed shortly after the Yankees got the results back from an MRI on Knoblauch's right elbow that has bothered him the past two weeks. New York placed Knoblauch on the 15-day disabled list after the game to make room for Sojo.

"Once we made the decision to disable Chuck, I called the Pirates and said let's do this deal," general manager Brian Cashman said.

Cashman said the MRI confirmed an earlier diagnosis that Knoblauch's has tendinitis and inflammation in the elbow. The move is retroactive to Aug. 3, and Knoblauch is eligible to come off the DL on Aug. 18. But Cashman said it was uncertain when Knoblauch would be healthy enough to return.

Knoblauch, making his first trip to the DL in his 10-year career, has missed nine games, including the last five, since injuring the elbow July 24, in Baltimore.

Knoblauch is hitting .291 with 60 runs scored this season and is a major part of the team's offense from the leadoff slot. Luis Polonia and Derek Jeter have shared that role lately, but Knoblauch's absence weakens the bottom of the lineup.

"He is a big piece for this team," Cashman said. "He is such a catalyst. He can get on base and stir things up."

Knoblauch has had problems in the field all year, making 15 errors. The Yankees have even used him at DH at times -- which will be more difficult with the acquisition of Jose Canseco -- and played the more sure-handed Jose Vizcaino at second.

Sojo, who spent four seasons with the Yankees, was batting .284 with five homers and 20 RBI for Pittsburgh. New York has shown an interest in him all season, and finally completed the deal.

"He was one of our leaders the last few years," manager Joe Torre said. "I know he'll be pleased coming back."

The Yankees sent minor league right-hander Chris Spurling to Pittsburgh. Spurling, 23, was 4-6 with a 3.79 ERA in 34 relief appearances for Class A Tampa.