FIELD umpire Alex Whetton has made an early exit from the Fremantle-Essendon clash at Optus Stadium after copping an accidental knock to the head from Docker Lachie Schultz. 

Whetton was the controlling umpire in the middle of Optus Stadium late in the second quarter when he changed direction and moved into the path of a sprinting Schultz. 

The pair clashed heads and Whetton tumbled to the ground, but not before putting his whistle to his mouth. 

FULL MATCH COVERAGE Fremantle v Essendon

The umpire lay motionless on the turf for several moments and was immediately attended by concerned players, trainers and medical staff. 

Whetton was eventually helped to his feet and walked from the field. He was replaced by emergency field umpire Daniel Johanson for the rest of the game.