Ryan Leaf, promoting his book, "596 Switch," earlier this month. (Dean Hare / AP)

There is no information on the type of Harrison’s tumor or what his treatment will be, although ESPN reported that the long-term prognosis for both his life and career “appear to be good.” He is not expected to play again this season and Lions Coach Jim Schwartz would say only that “it’s a privacy issue and I’m not going to comment on it.”

Leaf’s tumor, discovered when he complained of dizziness and blurred vision, was removed in a seven-hour procedure in May. In a chat with Seattle Times readers, Leaf, 35, revealed that he’ll soon begin six weeks of radiation treatment.

“I had most of the tumor removed back in May,” said Leaf, the No. 2 pick behind Peyton Manning in the 1998 NFL Draft. He retired after a failed pro career in 2002. “I’m very grateful and blessed that it was benign. I do have to go to Southern California and go through six weeks of radiation starting in the middle of November, but it’s just another bridge I need to cross.”

The discovery of Harrison’s tumor appears to be the result of a lucky series of events: He left the Philadelphia Eagles as a free agent in August and signed with the Lions, who used him infrequently. The Eagles went with Ronnie Brown and quickly soured on him after his poor decision to try a pass on the goal line in a game against San Francisco. The Lions, with Jahvid Best suffering another concussion, needed help at RB and preferred Brown to Harrison. The Eagles were happy to make a deal, doing so just before the trade deadline Tuesday. Harrison’s tumor was discovered by Eagles doctors during his physical and the trade was voided.

There is precedent for playing again. St. Louis Rams rookie defensive end Robert Quinn had surgery to remove a brain tumor during his senior year at North Carolina. (He was suspended for the season because he received improper benefits.)

The Eagles and Harrison’s agent declined to comment Thursday.