Thurston confirmed at the Cowboys' mid-year dinner in Townsville on Friday night that he would play on in the 2018 season after this year's representative swan-song.
But the jury is still out on whether Thurston will launch his 2017 representative farewell in May 31's Origin opener as he battles a shoulder injury suffered in the trans-Tasman Test.
Queensland coach Kevin Walters is set to give Thurston until May 28 to prove his fitness - just days before Origin I in Brisbane.
"Speaking to Kevvie, he's going to come out and say Sunday next week is the deadline for Johnathan," Queensland great and Origin selector Darren Lockyer told Nine Network on Friday night.
Thurston is confident of running out against NSW at Suncorp Stadium but admitted his 34-year-old frame was taking longer to get right.
"The older you get, the slower the body takes to recover," Thurston told the Cowboys website.
"You need to make sure you do everything in your power to get your body right.
"We've got a great medical staff here. (Cowboys physio) Steve Sartori knows my body better than anyone.
"We continue to work around the clock to get it right."
Thurston admitted he was relieved to finally announce his future.
"I am very blessed and lucky to have the career that I have had," the record four-time Dally M Medallist said.
"I had no intention of leaving.
"Now that the deal is done I can concentrate on my footy and helping my teammates on and off the field."
Co-captain Thurston said he would use his remaining time at the Cowboys to groom the next generation to ensure he left the club in great hands.
Rookie half Kyle Laybutt is expected to reap the most rewards but Thurston said he hoped to influence the entire team before his time was done.
"The club has been a big part of my life so I want them to be successful," he said.
"It's a role I really enjoy, passing on the knowledge on the younger boys around me.
"But I am there not just for the halves but any of the boys if they want to have a chat.
"I enjoy that part of the captaincy."
The three-time Golden Boot winner linked with the Cowboys in 2005 after three years at Canterbury where he won a premiership in his final year before leading North Queensland to their maiden 2015 title.
"For my life I had to get out of Sydney to not only better develop my footy but also myself as a person," Thurston said.
Photo: Photosport Johnathan Thurston