SAN DIEGO -- Pitcher Mark Worrell, who was believed to be the key piece to the Khalil Greene trade one year ago, signed a Minor League contract Thursday to remain with the Padres.

Worrell missed all of the 2009 season after having Tommy John surgery on March 25 to repair the ulnar collateral ligament in his right elbow.

Worrell, who on July 21 had ulnar nerve transposition surgery, has been undergoing his rehabilitation at the Padres' Spring Training facility in Arizona. The Padres think that he can start throwing in Spring Training and return sometime this summer.

Worrell was acquired by the Padres with a player to be named -- who ended up as rookie Luke Gregerson -- from the Cardinals on Dec. 4, 2008, for Greene.

Worrell, 26, was non-tendered by the Padres following the season and removed from the 40-man roster. Worrell suffered the injury during Spring Training.

Gregerson, of course, became the key piece to the Greene trade. The right-hander became a key figure in manager Bud Black's bullpen, going 2-4 with a 3.24 ERA in 72 games. He had a 0.65 ERA in 37 games at PETCO Park.