The Lions announced Friday that Harrison was placed on the reserve/non-football illness list, ending his season, after a physical with Philadelphia Eagles team doctors Thursday that revealed the tumor. The physical took place following the Tuesday trade that sent Harrison and a 2013 draft pick to the Eagles for running back Ronnie Brown.
The trade was voided after Harrison failed the physical.
"He was in very good spirits," Schwartz said. "But after that, I don't know if I want to talk too much. It's one of those things, it's a non-football thing, and I'll just let him take it away from that spot."
NFL.com's Steve Wyche reported Thursday that Harrison's tumor might not have been discovered had it not been for the physical. The Eagles did not say what caused their medical staff to examine Harrison's brain. Comcast SportsNet Philadelphia reported Thursday that Harrison told the Eagles he was experiencing headaches, which led to the tumor-finding MRI exam.
Multiple Lions teammates also told the Free Press that Harrison had been experiencing headaches, to the point that he wore sunglasses on the field during practice before being fitted with a visor.
"Everybody thought it was just a regular headache," cornerback Chris Houston told the paper. "It was much more than that."
The Associated Press contributed to this report.