The NRL has requested more information from Manly on the potentially career-ending injury to former NZ Kiwis centre Steve Matai, as the club applies for a salary cap exemption on medical grounds.

Last week, the Sea Eagles confirmed they had applied for medical retirement clearances for both Matai and fellow club veteran Brett Stewart, after they had failed to return to training ahead of the 2017 season.

The NRL has already rejected Stewart's case based on his ongoing knee injury, while the probe into Matai's neck and shoulder region is continuing, as the club looks to strike his wages from the cap.

It's understood Manly will need to point to a specific incident in which Matai sustained the current injury and that it is separate to any ongoing issues that have plagued his career.

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Complicating the case further for Manly is the fact the NRL doctor presiding over the matter is Paul Bloomfield - the same man who led Manly's medical department between 2000-12.

In that time, Matai regularly battled neck issues, since he missed a large portion of the 2007 season - just three years into his first-grade career.

However he managed to play almost three-quarters of Manly's games in each season after that, until last year, when he was injured in round nine and never resurfaced.

Injuries have dogged Matai since 2010, when he played the last of his 10 tests for the Kiwis.