The male casualty, who was in his 30s, suffered a "significant leg injury" due to a falling rock at the Scotia Winch Challenge 4x4 event near Aberfeldy.
Paramedics were called to the scene on Saturday, but were unable to reach the remote site in Griffin Forest.
A search and rescue helicopter had to be brought in to recover the casualty.
Police said the man was in a "stable but critical" condition at Ninewells Hospital in Dundee.
The event, which has taken place at Griffin Forest several times in previous years, sees 4x4s tackle tough terrain, navigating over boulders, tree stumps and steep slopes.
A man was flown to hospital after he was seriously injured at an off-road motorsports event in Perthshire.