Jarryd Hayne's surprise plan to quit the NFL to play for Fiji's rugby sevens team at the Rio Olympics may be over before it even starts.

Former Austaralian Sports Anti-Doping Authority boss Richard Ings appeared to punch a giant hole in the plan just hours after Hayne's shock announcement by saying the former NRL star would not be eligible under World Anti-Doping Agency (WADA) rules to compete for Fiji.

'Slight problem mate, World Rugby require you to be in their registered testing pool six months to be eligible to play,' Ings posted in a tweet after Hayne announced he was quitting NFL.

'If Jarryd Hayne had been playing in WADA compliant sport he would have grounds to reduce the six months, but NFL is PED badlands. No chance.'

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Jarryd Hayne announced his retirement from the NFL to join the Fiji rugby sevens team in the hope of making the Olympics but due to doping rules may not be able to compete according to the former ASADA boss

Hayne shocked the sporting world early on Monday by announcing he would retire immediately from the NFL after playing just one season with the San Francisco 49ers - and will try to join the Fiji rugby sevens team at the Rio Olympics.

'I am retiring from the NFL because the Fiji Rugby Sevens team reached out to me about the opportunity to join the team for the upcoming Olympics, and I simply could not pass that chance up,' Hayne said in a statement.

'The Olympics has been something I have admired since I was a little boy and it is an opportunity I feel very similar to me joining the NFL.'

Hayne, a former Australian rugby league champion, signed with the 49ers as an undrafted free agent on March 3, 2015.

He appeared in eight games, with one start, last season and had 52 yards on 17 rushes and also caught six passes for 27 yards. He returned eight punts for 76 yards.

'Jarryd is a tremendous example of what can happen when you commit to a goal and do everything in your power to make it a reality,' 49ers general manager Trent Baalke said in a statement.

Former Austaralian Sports Anti-Doping Authority boss Richard Ings appeared to punch a giant hole in the plan just hours after Hayne's shock announcement by saying the former NRL star would not be eligible to play

Hayne, a running back, said the opportunity to play rugby sevens for Fiji in this year's Rio Olympics prompted the decision

Hayne, a former Australian rugby league champion, signed with the 49ers as an undrafted free agent on March 3, 2015

'He earned the right to wear a 49ers uniform and compete alongside the best in the game.

'We fully support Jarryd's decision to pursue another dream - representing the Fiji Rugby Sevens team in this summer's Olympic games.

'We look forward to watching him in Rio and wish him continued success.'

The Australian-born Hayne was a star in the National Rugby League competition in Australia from 2006-14 before joining the 49ers.

Though born in Australia, his father is from Fiji.