The latest Hankook Ilbo poll shows that frontrunner Lee Myung-bak's support rate will fall to as low as 29.3 percent if he is confirmed to be involved in a stock manipulation scam.
Even though he will maintain the lead, independent rightwing candidate Lee Hoi-chang's rating will rise to 22.7 percent.
The election results will be uncertain up to the last minute as 24.3 percent will remain as undecided voters, the poll showed.
Liberal candidate Chung Dong-young's rating will jump to 15.9 percent if the former Seoul mayor is found guilty of the stock manipulation scandal.