Valentine Holmes has delivered a farewell message to Sharks teammates and fans hours after being granted a release from the final year of his contract to chase an NFL dream.

The talented fullback, who also played for Queensland and Australia during a stellar 2018 season, shared his thoughts on Instagram.

"Today I have announced my decision to pursue a career in the NFL. Firstly I would like to thank my teammates, coaching staff and everyone at the @cronullasharks Club for their support," he posted.

"I would also like to thank the fans for your ongoing support through my last 6 years at the club. It is the fans who make our game so special and I hope you continue to support me on my new journey."

Earlier on Tuesday, Holmes asked Sharks fans to understand his decision in a statement posted on the Sharks' website.

"I will be forever grateful to the Cronulla Sharks Football club and the Sharks fans for the past five years of support, it was a special moment we all shared winning the club's first ever NRL premiership," he said.

"I understand this decision may come as a shock to many but I personally believe it's the right time for me to challenge myself and pursue this NFL opportunity.

"Hopefully the fans can understand and support me as they have done throughout my career."

If Holmes fails to land an NFL contract and returns to rugby league, he must play for the Sharks in 2019. 

If his NFL dream fails to materialise, he will be an NRL free agent for the 2020 season and beyond as per his existing contract.

Sharks CEO Barry Russell said the club understood Holmes's decision.

"We are incredibly saddened to see him leave our club and exit the game of rugby league, however, we wish him all the best in pursuing his NFL career and hope one day he may again wear the Sharks colours," he said.

Holmes will be hoping to follow the on-field exploits of Jarryd Hayne, who left the Eels in 2015 to spend time with the San Francisco 49ers.

Hayne played eight NFL matches for the 49ers for modest returns before returning to league following a short-lived stint with the Fijian sevens rugby side.

NRL CEO Todd Greenberg said players often come back to the sport quickly when they try their hand at other sports.

"It's a big risk for a young player in our game, who gets paid significantly, to try his hand at a new sport," Greenberg said at the launch of Magic Round in Brisbane on Tuesday.

"I'm not concerned about losing players to other sports ... players are desperate to play in the NRL."