Sonny Bill Williams says he would welcome the chance to fight Paul Gallen and Barry Hall as he seeks to reignite his boxing career.

The 36-year-old retired from rugby league and rugby union in March this year after a stellar career that saw him win two NRL premierships and two rugby World Cups with the All Blacks.

Williams' first foray into boxing was in 2009 and he has won all eight fights he has contested.

Just months after his retirement from rugby, he narrowly defeated Waikato Falefehi in a low-profile fight in Townsville in his first outing in the ring in six years.

After that fight, Williams said he hoped to take on Hall once he was less rusty and had a couple more fights under his belt.

Now the former code-hopper has doubled down on his desire to fight the likes of ex-football stars Hall and Gallen. Any clash between Williams and one of Gallen or Hall would be sure to attract a massive audience.

When asked if he would like to fight Gallen, Williams said he would be more than capable of taking it up to the former Cronulla Sharks captain.

"I hope you weren't insinuating that he's (Gallen's) out of my league, because for myself I definitely don't believe that," he told ABC Radio on Saturday.

"He'll be all part of the process. For me it's the challenge."

Williams also took a thinly-veiled swipe at Gallen, saying he only fights "for the money".