The club announced Wednesday night that Jon Niese, still a rookie and a prospect, will be promoted from its Triple-A Buffalo affiliate to take Perez's place in the rotation and on the roster and that Perez had been assigned to the disabled list because of patellar tendinitis in his right leg.
Niese, not 40-year-old rookie Ken Takahashi, now is to start against the Pirates on Friday, and Perez, exiled from the rotation Sunday after a dreadful performance against the Phillies the previous day, is to begin rehabbing his leg in Florida at the Port St. Lucie complex.
The club had said Takahashi would make the start Friday, but general manager Omar Minaya said Wednesday night he preferred to "keep the bullpen in order" by retaining Takahashi as a reliever. Moreover, the Japanese pitcher hadn't throw more than 55 pitches in any appearance in Triple-A before he was promoted last week.
Perez was examined via MRI on Wednesday. The examination detected the cause of pain he has experienced near the knee cap since some point in Spring Training. The problem, Minaya said, had been noted on the club's daily medical report all last week. But it never was mentioned publicly or noticed -- even by some teammates -- until Sunday, when the 27-year-old pitcher began wearing an ice pack on his knee. At that point, manager Jerry Manuel said Perez would have continued pitching if not for his ineffectiveness.
Now Perez will have opportunity to recover and pitch on the Minor League rehab program. The date of his return to the big leagues is undecided.
Niese, who is left-handed and 22, had struggled in his first four Triple-A starts, producing an 8.44 ERA and an 0-2 record. He allowed three hits, a walk and a run and struck out eight in a six-inning no-decision against Louisville on Friday. He had a 1-1 record and a 7.07 ERA in three starts and 14 innings last season, pitching eight scoreless innings against the Braves on Sept. 13.
Marty Noble is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.