"Just wasn't feeling well and we just thought it was best to hold him back today. But we fully expect him to be back out here tomorrow," Frazier said. "Maybe a virus. He should be fine."
Frazier said from everything he's been told, Harvin's issue on Thursday was not related to the migraine headaches that have plagued him since childhood.
"If you're complaining about stomach, other things, there's a difference," Frazier said. "We've gone through the migraine part. We know there's a distinct difference between what's happening with your stomach and what's happening with migraines."
Harvin has missed three games in his two-plus seasons with the Vikings – all because of migraines or migraine symptoms. He missed Week 13 and 14 games last year against Buffalo and the New York Giants, and also missed a Week 14 game in his rookie season against Cincinnati.
Harvin told the Virginian-Pilot this summer that doctors he was meeting with found something with his neck that might have been contributing to the migraines and also changed up his diet. He said in August that he had been migraine-free all year.
Harvin also collapsed last fall on the practice field because of a reaction to the medication he was taking for them at the time. He was taken to the hospital in an ambulance and spent the evening there.
The Vikings have been answering questions this week about the lack of snaps Harvin received last week (he was on the field for less than half of the offensive snaps), but offensive coordinator Bill Musgrave said Thursday the coaching staff was looking to expand Harvin's role.
"We definitely want to expand Percy's dynamic ability. We want to do a lot of good things in all packages," Musgrave said. "Certain packages Percy's a part of and certain packages he's not. We want to play to his strengths. He's so dynamic and plays with such passion that we want to get effectiveness and get good bang for our buck when he is on the field."
Harvin was the Vikings' leading receiver last year, catching 71 passes for 868 yards and five touchdowns and set a team record for the most combined net yardage in a player's opening two seasons with 3,922 yards, breaking Adrian Peterson's previous mark.
Musgrave said Harvin's absence on the field Sunday had nothing to do with his blocking ability, calling him "one of our best blockers."
"We'll look for Percy to be out there as often as we can get, of course," Musgrave said.
Tim Yotter is the publisher of Viking Update. Follow Viking Update on Twitter and discuss this topic on our message boards. To become a subscriber to the Viking Update web site or magazine, click here.