For the second time in three seasons with the Seattle Sounders, central defender and team captain Danny Jackson could have his season cut short with a knee injury.

Jackson, who recently returned from a second tryout with Major League Soccer's Kansas City Wizards, planted awkwardly Saturday on the second day of training camp, possibly ending his season before it starts.

The initial prognosis was a torn ACL and MCL, but a second opinion from team doctor Steven Bramwell determined Jackson would need exploratory surgery. Jackson, 25, arguably the best defender in the USL First Division, will undergo the arthroscopic surgery and have Bramwell repair the damage, if necessary, on Tuesday.

In 2003, Jackson tore the ACL and lateral meniscus of his left knee during practice with four matches remaining. It took him about seven months to fully recover after having surgery.

Sounders trainer Anne Taylor and Bramwell consider that in a worst-case scenario, recovery could take eight months or more, assistant general manager Bart Wiley said.

"That puts us thin at the back for sure," Sounders coach Brian Schmetzer said. "We've got to replace him. I just feel terrible for Danny Jackson. Realistically, we're looking for him to recover in time for MLS camps next season.

"He's a young man with a bright future, but now he's got another major setback to come back from."

The English-born Jackson, who won an NCAA national championship with North Carolina in 2001, was named the Sounders' team captain for 2005 on the first day of training last Friday.

Jackson could not be reached for comment yesterday.

"We'll know a lot more after next Tuesday's knee scope," Taylor said.

Jackson anchored a Sounders defense that keyed a big run to the A-League championship match last season and was named the club's Defensive Player of the Year. Seattle lost to the Montreal Impact 2-0 in the title match.

Aside from Jackson, the Sounders have five players under contract who can play defender in veterans Kevin Sakuda, Billy Sleeth, Ryan Edwards, Scott Jenkins and Zach Scott.