"Even though you would like to stick it in a box and have it be fixed this way, history has told us that migraines aren't that way."
The Vikings travel to San Francisco for a preseason game against the 49ers on Sunday, however, Harvin will not travel with the team, and it is unknown when he will be able to play.
The former first-round draft pick was second among Vikings receivers with 60 receptions and 790 yards in his rookie campaign last season.
(Reporting by Mike Mouat in Windsor, Ontario. Editing by Steve Ginsburg)