NASHVILLE, Tenn. (AP) -- Tennessee offensive coordinator Mike Heimerdinger has been diagnosed with cancer and is expected to start chemotherapy treatment almost immediately.

Coach Jeff Fisher announced Wednesday that Heimerdinger has been very sick the past three weeks but learned the diagnosis Wednesday morning. Heimerdinger wasn't at practice.

Fisher declined to specify what type of cancer Heimerdinger has but asked for prayers for both the coach and his family.

The Titans (5-5) visit Houston (4-6) on Sunday.

Fisher says he doesn't know if Heimerdinger will be back this week or help coach Sunday's game. Fisher says quarterbacks coach Dowell Loggains likely will call plays. Offensive line coach Mike Munchak will oversee the run offense.