And Cronk, 33, is unsure of his playing future after announcing he will leave NRL club Melbourne and join his fiancee in Sydney in 2018.
But Walters believed it was "irrelevant" whether this would be the pair's Origin swan song.
He simply wanted them to bring their best tonight as the Maroons look to keep their dynasty alive.
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Walters said Queensland would need Slater and fellow "Big Three" members Cronk and skipper Cameron Smith to shine if the Maroons were to clinch their 11th series win in 12 years.
"They haven't given any indication to anyone really," he said.
"That's irrelevant. We just need them to be at their best to win. They know what is going on but we just want the best out of them tomorrow night and worry about that next year."
A controversial game one omission, Slater reclaimed his Queensland No 1 jersey for the first time in two years in Origin II to help inspire a come from behind 18-16 win in Sydney.
"I think Billy made a big difference in game two and we need that difference again for Queensland to get home," Walters said.
"I think Cooper Cronk can add to that as well regardless of whether it is their last game for Queensland."
