Under-fire Essendon midfielder Zach Merrett was suffering a virus when he took the field against Greater Western Sydney on Sunday at Giants Stadium.

The 23-year-old managed to get up to play the game but put in a below-par performance, collecting just 16 disposals and applying little pressure.

Zach Merrett was battling illness in round one. Credit:AAP

Merrett's effort was the subject of much discussion after the game and one particular contest midway through the first quarter drew heavy criticism from former club greats such as Tim Watson, who described it as "not up to AFL standard".

The Bombers cleared Merrett to play, aware that he had worked his way through such issues at other times during his 104-game career, however he struggled during the match.