Packers receiver Geronimo Allison was knocked out cold after a vicious collision with Lions defensive back Tracy Walker.  There was a flag thrown for the helmet-to-helmet hit.

The defensive back appeared to be attempting to intercept the pass at the time of the unfortunate collision. 

After laying motionless on the field for a few moments, Allison was eventually able to walk off under his own power for medical attention. 

Flip the Page to see Allison get knocked out: