Steve Trachsel, who has pitched more than 173 innings in each of the last nine seasons, could miss up to six months after it was learned the veteran right-hander has a herniated disc.

Trachsel, who was expected to be the Mets No. 4 or 5 starter entering the season, on Wednesday saw Los Angeles-based back specialist Dr. Robert Watkins, who performed tests on the hurler. MRI and X-rays performed Sunday initially disclosed the disc problem.

Sources indicated that surgery is likely, and if Trachsel undergoes the procedure, he could miss at least six months. If surgery is not deemed necessary, Trachsel could miss as little as three months.

General manager Omar Minaya did identify the pool of possible replacements for Trachsel as Matt Ginter, Jae Seo and Aaron Heilman, each of whom started for the Mets last season, and Francisco Campos, who pitched in the Mexican League as well as Triple-A with the White Sox organization. Each pitcher in the pool is right-handed.

Trachsel has been a workhorse with the Mets since joining the club prior to the 2001 season, starting at least 28 games in each of his four seasons in New York. Last season, Trachsel was 12-13 with a 4.00 ERA in 33 starts, which tied for the team lead.