MELBOURNE, Australia — International and Australian sports stars began pitching in this weekend to help relief efforts in flood-ravaged Queensland state.

Roger Federer and Rafael Nadal will headline a special sold-out “Rally for Relief” event at Rod Laver Arena in Melbourne on Sunday, a day before the start of the Australian Open.

The floodwaters that swamped entire neighborhoods in Brisbane, the state capital, left behind a thick layer of putrid sludge and affected more than 30,000 homes. Weeks of rain and flooding across Australia’s northeast have left 26 people dead and 20 more missing.

“When I saw it hit the city of Rockhampton, I right away thought of Rod Laver,” Federer said of Laver’s birthplace. “I tried to reach out to him and see if he wanted to do anything, if he needed my help. Once I came down to Australia, I spoke to him.

“It’s very appropriate and a must for us to do something as a tennis family really. I’m really happy we’ve been able to do it again,” he added.

Players competing Sunday will also donate the shirts they wore in the exhibition in a “Shirts off their Backs” auction that is expected to raise thousands more for the flood appeal, and buckets will be passed around to collect donations.