Hamburg, Germany -- (Sports Network) - The WBA heavyweight title fight between champion Ruslan Chagaev and challenger Nikolay Valuev, scheduled for May 31, has been postponed.

According to Universum Promotions, Chagaev is suffering from a viral infection of the upper respiratory tract and is being treated with antibiotics.

The fight has yet to be rescheduled.

Chagaev (24-0-1, 17 knockouts) took a split decision over the 7-foot Valuev (48-1, 34 KO) to win the title in April of 2007. Valuev has won a pair of fights since losing to Chagaev, who has made just one title defense -- winning a unanimous decision against Matt Skelton this past January.