But the devastated Canberran says being ruled out of Australia's World Cup campaign is the toughest part to swallow after scans revealed he would need shoulder surgery this week.

Fairfax Media can reveal Mills will have an operation to repair the torn rotator cuff in his right shoulder - his shooting shoulder - after he carried the injury for most of the San Antonio Spurs' NBA title-winning season.

He could miss up to four months of the 2014-15 NBA season.

It's a massive blow for the 25-year-old just two weeks after basking in championship glory and on the same day he tests the NBA free-agency market for the first time.

Mills said his enforced layoff could affect his next move, after experts predicted he could receive offers of up to $5 million.

He is yet to decide whether he will stay with the Spurs or sign a deal with a rival franchise, but the former Canberra Marist College student said the layoff would make him hungrier to succeed.

"I haven't been through free-agency before, having this injury changes everything again," Mills told Fairfax Media.

"I have no idea how it works, but I'm guessing it will affect [my next deal]. But it's out of my hands. It is what it is. We've got to make the most of the situation and move on."

It's the first time Mills is testing his worth on the open market and he was poised for a multi-million dollar deal before injury hit. Mills says he will weigh up his options before deciding on his future.

Mills starred as the back-up guard for Tony Parker in the Spurs' triumphant campaign and coach Gregg Popovich said Mills was crucial to San Antonio's title run.

His performances, including a defining 17-point run in the championship-winning game, put him on the radar of teams, including the New York Knicks.

Mills had the best season of his five-year NBA career with the Spurs, averaging 10.2 points a game in the regular season and going on a scoring spree in game five of the NBA finals to lift San Antonio to the title against Miami Heat.

But behind the scenes he was managing a wear and tearshoulder problem and it wasn't until scans were taken this week that the effects hit home.

"It was a shock, I didn't know it would be this bad," Mills said.

"You think nothing can deflate you [after winning a championship]. I had to find a way to process the injury news and what's going to happen. It's not until now that it's sinking in.

"It's going to be a brutal recovery process. I'll go straight into surgery, but I'm told the next four to six weeks I won't be able to do anything, and it will be brutal."

Mills is shattered that he will miss what looms as Australia's best chance to win a medal at a major international tournament.

Australia will play in the World Cup in Spain from August 30 to September 14, with the Boomers boasting NBA players Matthew Dellavedova, Aron Baynes, Dante Exum and Cameron Bairstow, as well as European star Joe Ingles.

"Missing the Boomers is the toughest of it all, I have a tremendous amount of pride to play for Australia," Mills said.

"This is a huge year for the team ... It's an exciting time and I've told the boys I'm going to be involved in anyway I can. I have all the faith in the world this team can go and get something done."

Mills' career has been plagued by disruptive injuries. He broke his hand before going into the NBA draft in 2009, broke his foot while training with the Portland Trail Blazers, and injured his hamstring in China on a playing stint during the NBA lockout in 2012.

"It's just another hump in the road, some more adversity that I've got to deal with," Mills said.

"I've dealt with things before, but not like this. It's going to be tough, but it's going to build my character and make me a stronger person. I'm going to come out of this more hungry and determined."