Pittsburgh placed Sepulveda on injured reserve Saturday and signed Jeremy Kapinos to take his place.
It is the third time Sepulveda's season has ended early. He missed the entire 2008 season and the second half of 2010 with a similar injury. Sepulveda was averaging a career-best 46.1 yards per punt this year.
Kapinos averaged 41.1 yards per punt after signing with the Steelers to replace Sepulveda last year. He narrowly lost out to Sepulveda during training camp and was one of the final cuts before the roster was set at 53.
Kapinos will be in uniform Sunday when the Steelers face rival Baltimore.