Instead, doctors found the problem. And while the trade was voided, the much bigger picture is that Harrison learned about a serious ailment that can be treated.
The Eagles declined to comment on Harrison on Thursday since he is again a Lion. His agent did not return a call seeking comment. Harrison, 28, did not practice Thursday. The Lions injury report listed him as out with an "illness." Lions head coach Jim Schwartz would not discuss the player's health.
"It's a privacy issue, and I'm not going to comment on it," Schwartz said, according to the Detroit Free Press. "He's back on our 53-man roster."
There were few details about the tumor - no public reports said whether it is benign or malignant - but brain tumors can often be treated. Depending on the type of tumor, surgery, radiation or chemotherapy could be used.
If it can be treated with only surgery, "the success rate is very high, especially if it is benign," said Rodwan Rajjoub, medical director of neurosurgery at Susquehanna Health Systems in Williamsport. "Usually the effect from surgery is very minimal."
Malignant tumors can also be treated, though the prognosis depends on the exact type.
Brain tumors, even benign ones, can develop into adulthood and may go undetected for years, Rajjoub said. They are often found after a patient exhibits symptoms such as weakness or headaches.
Harrison played in Philadelphia last season but was allowed to leave as a free agent. He had few opportunities to play in Detroit, though, and was happy when the Eagles moved to reacquire him Tuesday.
"I'm excited to be back," Harrison said in comments released by the Eagles after the trade.
The Lions, whose starting running back, Best, is dealing with a concussion, worked out former Eagles running back Eldra Buckley, according to reports from Detroit.
Void for Vick? Although it can't be made official at this point, Michael Vick has essentially voided the sixth year of his contract, as expected.
If the quarterback was to play more than 35 percent of the Eagles' snaps in any year of the $100 million contract he signed in August, the sixth year, worth $20 million, would be voided. Vick has already played in 379 of 406 offensive snaps for the Eagles this season. Projected, the Eagles will have 1,082 plays over the 16-game season.
If Vick wasn't to play another snap this season, he still would have played exactly 35 percent of the Eagles' snaps based off the projected number of snaps.
Contact staff writer Jonathan Tamari at 215-854-5214, firstname.lastname@example.org, or @JonathanTamari on Twitter.
Inquirer staff writer Jeff McLane contributed to this article.