A second training collision in three days has put jinxed Wallabies halfback Will Genia in doubt for Saturday night's Tri-Nations decider against the All Blacks.

In a major scare, Genia will have to wait to be given the green light by team medics on Friday after copping another head knock, this time from reserve lock Rob Simmons, in Australia's Thursday training session at Ballymore.

The influential No.9, regarded by former Wallabies captain and new Hall of Fame inductee Paul McLean as nigh on irreplaceable, believes he "should be fine" but was left seething after his latest mishap.

Despite both wearing non-contact bibs, Queensland Reds teammates Genia and Simmons ran straight into each other as they chased a high kick in one of the last plays of training.

The suspected concussion concern comes just two days after another towering Reds forward, Radike Samo, split Genia's head open and left him dazed after charging into him in another highly-physical session.

Losing Genia would be a massive blow for Australia who are looking to end a decade-long Tri-Nations drought at Suncorp Stadium.

Not only is the 23-year-old the Wallabies attacking general, Genia's back-up Luke Burgess has not played for two months due to a broken hand.

Burgess has been back on the Australian bench for their last two Tests but has not seen a minute of action as coach Robbie Deans kept Genia on the field.

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