The TAB is bracing for its first seven-figure payout on a single race if Pierro wins Saturday's Doncaster Mile at Randwick.

The wagering operator's media manager Glenn Munsie said a win by the $2 favourite would produce an unprecedented result.

"Pierro winning is a seven-figure loser for us," Munsie said.

"Much of that is through doubles.

"One punter had $10,0000 on the double of Miracles Of Life in the Blue Diamond coupled with Pierro in the Doncaster.

"There have been other substantial doubles with the Golden Slipper winner Overreach into Pierro.

"It's our biggest ever stand."

Despite the possible loss, Munsie advised punters Pierro would drift from his $2 quote on Tuesday by race time.

"Pierro will start longer," he said.

"The corporate bookmakers will not let a horse go round at $2 in a 20-horse field."

If he does win, Pierro will be the shortest-priced favourite to do so since bookies were stung in 1999 when the great mare Sunline won her first of two Doncasters after being backed from $2.80 to $2.10 on race day.