Buenos Aires, Argentina -- (Sports Network) - Nikolai Valuev will face off with John Ruiz for the vacant WBA heavyweight title before August 31.

The WBA made the decision after current champion Ruslan Chagaev was forced to pull out of his mandatory title defense against Valuev. Chagaev ruptured his Achilles' tendon in training last week.

The representatives of both fighters have been given until July 15 to find a solution as to who will stage the fight. Should they fail to reach an agreement, a purse bid will be called.

The bout will mark the second time Valuev and Ruiz will battle. The two heavyweights met in Germany during December of 2005 when Valuez outpointed Ruiz.

Meanwhile, the WBA named Chagaev "champion in recess," and he will be given the chance to challenge the new, regular champion until June 26, 2009. To do so, however, he will need to document his medical condition to the WBA.