Valuev claimed a majority points win over 12 rounds
The World Boxing Association (WBA) is to investigate Nikolay Valuev's victory over Evander Holyfield on 20 December.
The Russian retained his heavyweight crown with a majority points decision over the veteran American, although the result was questioned at the time.
"The Championship Committee have ordered a panel of judges to review the tape of the fight between Valuev and Holyfield," said a WBA statement.
Holyfield, 46, was bidding to become the oldest ever heavyweight champion.
He was also hoping to become the first five-time heavyweight champion, but was beaten in Zurich, Switzerland.
Two judges had the fight 116-112 and 115-114 with the other scoring it even.
"I saw it the other way from the judges but I'm not disappointed by my performance," Holyfield said after the fight.
Holyfield said he would consider his future in the sport after the defeat.
The WBA has given no specific date for a decision on their investigation only saying it will be made in "the following weeks".