The Portland Timbers today announced that forward Jose Adolfo Valencia will undergo surgery to repair damaged cartilage in his left knee. Valencia is expected to miss 6-12 months.

A recent MRI showed damaged cartilage to the surface of the femur in Valencia’s knee. The surgery will be performed by Timbers Director of Medicine Dr. Jonathan E. Greenleaf at Sports Medicine Oregon on Monday.

While it is uncertain when Valencia, 20, sustained the injury, the Timbers and Valencia’s former club, Colombian first-division side Independiente Santa Fe, have agreed to amended terms of the original loan agreement. Valencia’s designation as a Young Designated Player was contingent upon the terms of the original loan agreement. The new loan agreement terms do not require him to count as a Young Designated Player this season. Valencia will remain with the Timbers on their Disabled List while rehabilitating from surgery and therefore not occupy a spot on the team’s roster nor count as one of the team’s international players.

“Our No. 1 priority is ensuring the long-term physical health of Jose,” said Gavin Wilkinson, general manager of the Timbers. “We are pleased to have worked with his former club in Colombia on amended terms of his transfer, considering the circumstances. We are very committed to Jose as a person and as a player, and intend to return to the original terms of his transfer agreement when he returns to full health following rehabilitation.”

Valencia, who was originally acquired from Independiente Santa Fe on Dec. 15, 2011, will conduct his rehabilitation with the team in Portland.

“We feel strongly about our long-term commitment to Jose and see him as a big part of the future success of this team,” Wilkinson said.