Sharks said it was a "great disappointment" after they had been working  to re-sign Holmes on a five-year deal to make him the highest paid player in club history.

"While this is in no way the outcome the club planned for, there was no option but to grant a release to Holmes," the club added in a statement.

Under the terms of the release, if Holmes is unsuccessful in the NFL and wants to return to the NRL in 2019, it can only be with Cronulla Sharks, and Valentine will not be eligible to play for any other NRL club during 2019.

Holmes hailed the Sharks for their understanding and support of his decision, and said he would have fresh discussions with the Sharks about his career if his pursuit of an NFL career doesn’t work out.

“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," the club quoted him as saying.

“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.”

Sharks CEO Barry Russell added: “While disappointed by Val’s decision, I acknowledge he has been outstanding for our club and for the game of rugby league.

“He is loved by our club, corporate partners, members and fans.

“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.”