SAN FRANCISCO (AP) _ Armando Rios' first three days with the Pittsburgh Pirates couldn't have gone much worse.

Rios, acquired in a four-player trade with the San Francisco Giants on Monday, found out Thursday he will miss the rest of the season with a torn ligament in his left knee.

Rios, hitting .260 with 14 homers and 50 RBIs, was placed on the 15-day disabled list.

``It's heartbreaking for me, and it's definitely tough for the team,'' Rios said. ``They make the trade, and they totally expect you to be out there. You just hate to see these guys out there every day playing hard, and you have to watch them from in here.''

The Pirates' new right fielder played his first game for Pittsburgh on Tuesday _ bobbling a ball in the outfield that allowed San Francisco to score the winning run in the 11th inning.

He twisted his knee in that game, then was seriously injured on Wednesday night when he fell awkwardly on a botched fielding play. As second baseman Warren Morris dropped a popup in the swirling winds at Pacific Bell Park, Rios fell in front of him and stayed on the ground, holding his knee.

An MRI exam revealed the torn ligament. Rios had the so-called ``Tommy John'' surgery on his right shoulder during the past offseason, but returned in time to start the season in right field with the Giants.

``Right now, I need to get out and do whatever the doctors say,'' Rios said. ``If I need surgery, then I get it done and get rehabbing, so I can get strong for next year.''