England and New Zealand will be on a collision course that may end in the courtroom should Eddie Jones seek to select Brad Shields for the summer tour of South Africa in a dispute that is set to threaten World Rugby’s authority as arbiters of the global game.

New Zealand have threatened to block England from picking Shields for the three-Test series against the Springboks – and believe they have legal basis for doing so – after it was first revealed by the Guardian that Jones will have permission from the Rugby Football Union to call on the Hurricanes flanker. It is understood however, that regardless of New Zealand’s threat, England still believe they would be entitled to pick Shields in accordance with World Rugby regulations.

The RFU has a policy of not selecting players based outside England but is willing to make exceptions for players who have agreed moves to England. The New Zealand-born Shields is due to join Wasps next season but not until he has finished his commitments with the Hurricanes, meaning he could play up to six Super Rugby matches after England’s tour.

World Rugby’s regulation nine states that all players must be released for international duty in the official June and November Test windows but New Zealand claim that a clause in Shields’ contract – known as Schedule Three – means they do not have to release him to England. All Super Rugby players in New Zealand who have not been captured by another nation are obliged to sign Schedule Three – which states the player in question is only available to play for New Zealand teams – as part of their NZRU contract.

“I don’t think you should jump to the conclusion that he will be available from our point of view,” the New Zealand Rugby chief executive, Steve Tew, said. “He has signed to New Zealand and he is contracted to play for New Zealand teams until the end of Super Rugby.

“We have a New Zealand player who is contracted to be here until the end of that competition and that would be our expectation. We are obligated to release players who have signed to play for other countries so they have made themselves unavailable for New Zealand. We always make sure that occurs and that is of particular relevance to the Pacific countries. But in this instance, Brad has signed a contract that makes him available for New Zealand teams.”

When asked last week if the Hurricanes would be obliged to release Shields if England wanted to select him, the Guardian was told by World Rugby that was “absolutely the case”. With New Zealand insisting they will invoke Schedule Three however, World Rugby has refused to comment aside from stating that it will not get involved in regulation nine matters unless requested to do so by a union.

According to World Rugby therefore, the ball is in England’s court. England are of the opinion that if they wish to select Shields they can do but if New Zealand dig their heels in, World Rugby will be forced to step in and try and broker a peace deal. If the governing body sides with New Zealand rather than enforcing its own regulation, it would set a dangerous precedent with regards to player release. It has been reported in New Zealand that Schedule Three has never before been challenged.

Jones is yet to publicly state if his wishes to select Shields – a 27-year-old flanker who qualifies for England through his parents and who has captained the Hurricanes to the top of the Super Rugby standings – for the South Africa tour, but with Courtney Lawes and Nathan Hughes both injured, the temptation would be obvious.

Despite the RFU’s policy of not picking players based outside England, Jones will have the green light to select Shields because his superiors consider Piers Francis as the precedent. Francis was picked for England’s tour of Argentina last summer when contracted to the Blues of Super Rugby and briefly returned before his move to Northampton.

Meanwhile, Northampton lock Christian Day will retire from professional rugby at the end of this season and begin a new role as a full-time player liaison officer with the Rugby Players’ Association from July.

“After 17 years of professional rugby, time has caught up with me, but I am extremely proud to have contributed so much at Franklin’s Gardens in ten seasons as a Saint,” Day said. “I have been battling an injury for some time which will unfortunately prevent me from playing in this season’s remaining fixtures.”

Joseph out for six months

Jonathan Joseph will miss England’s summer tour of South Africa because he requires surgery on the foot injury suffered in Bath’s heavy defeat by Saracens last weekend. Joseph was injured in a collision with Schalk Burger and hobbled back to the Bath bench on crutches.

Joseph is now expected to be sidelined for around six months and is now likely to miss the start of the season. It is a blow for Eddie Jones, who has started Joseph in 21 of his 28 Tests in charge and all the more so considering the England coach is already without Courtney Lawes, Nathan Hughes and Anthony Watson owing to injury, while Dylan Hartley, has not played since the end of the Six Nations because of concussion.