Spokesman Kent Brown said Thornton underwent tests at a local hospital after being carted off the field during the third quarter. Brown says all the tests were negative.
No timetable has been set for Thornton's return, but Illinois' bye week will give him a chance to heal and to be further evaluated.
Thornton was blocking ahead of running back Mikel Leshoure when he appeared to drop his head and make helmet-to-helmet contact with a Northern Illinois defender.
Thornton spent several minutes laying still on the field as medical personal strapped him to a stretcher. The 6-5, 310-pound sophomore from Oberlin, Ohio, was driven away on a cart.
Information from The Associated Press and ESPN.com's Adam Rittenberg was used in this report.