It is suspected that the man, believed to be aged in his thirties, fell from the bike on a dirt track at Wondai.
A passer-by made the discovery earlier this afternoon.
The RACQ CareFlight Rescue helicopter from Toowoomba’s Clive Berghofer CareFlight Centre was tasked to the Wondai school oval shortly before 2pm.
He is in a critical condition.
No further details are currently available.