Starter Matt Birk is planning to have arthroscopic surgery on his left knee during the next few days, his agent, Joe Linta, told The Associated Press on Wednesday.
Rabach, who required offseason surgery for a shoulder injury sustained near the end of the 2010 season, was told he would need another two to three weeks to heal, according to the newspaper. He and the Ravens had come to terms on a two-year deal.
Linta said Birk, a six-time Pro Bowl selection, should be able to return in a few weeks. Birk played in all 16 games for Baltimore last season despite having knee problems.
Birk, 35, has not practiced with the team this week, but he hopes to be ready for the Sept. 11 opener against the Pittsburgh Steelers.
The Associated Press contributed to this report.