Michael Dunlop, who has claimed three wins in the 2010 Southern 100, has been taken to hospital after a crash in the Solo Championship race.
With victories in the opening 1000cc event, Tuesday night's 60cc race and this morning's 600cc contest, Dunlop was a favourite for honours in the traditional finale to racing around the 4.25-mile Billown circuit.
The red flag came out on lap five and organisers confirmed it was due to an incident involving Dunlop.
He was taken to the Isle of Man's Noble's Hospital, but the organisers said there were no apparent injuries and the trip to hospital was for precautionary check-up only.
The Solo Championship race will now be decided over two four-lap legs, with the result based on aggregate times. The second leg will run after the sidecar championship race.