Patrick Tuipulotu of the All Blacks has been absent from the rugby field since being sent home from the end of year tour for "personal reasons."

All Blacks lock Patrick Tuipulotu is believed to be taking time out from rugby after testing positive to a prohibited substance.

Tuipulotu missed the All Blacks final end of season tour match in Paris last year, heading home immediately for what coach Steve Hansen described as personal reasons.

Two months on Tuipulotu is still absent from his Super rugby team the Blues, who played their first preseason match against the Hurricanes in Auckland on Saturday, for the same reasons.

SIMON WATTS/GETTY IMAGES Patrick Tuipulotu has made a big impression in his short career as an All Black.

It is believed Tuipulotu tested positive to a banned substance at some point last year and results were discovered in the lead-up to the final test of the season against France.

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HANNAH PETERS/GETTY IMAGES Tuipulotu at a training camp in 2014.

No punishment has yet been handed down as the process is thought to be on-going, with suggestions the results of the 'B' sample are not yet known.

It is also understood that circumstances surrounding the case are of a sensitive nature.

Tuipulotu is not thought to have used recreational drugs.

The 24-year-old is receiving advice from the New Zealand Rugby Players' association, and other experts. He could face a ban that would see him miss at least the entire 2017 season, but it's believed he is continuing to investigate options and may yet escape penalty on compassionate grounds.

Tuipulotu, who is signed with NZ Rugby through to 2019, had double hip surgery on a debilitating birth defect in 2015, which saw him miss the Rugby World Cup. He has played 12 tests, and is a major loss for the Blues.

When approached for comment, Tuipulotu's agent Ben Boyle would only say it was a personal matter.

A NZ Rugby spokesperson said: "(Tuipulotu) is dealing with a personal issue and we're not at liberty to discuss any further."

Players' Association boss Rob Nichol and Drug Free Sport NZ echoed the sentiments, saying they were not at liberty to discuss any details further.

World Rugby confirmed that it is automatically informed of positive tests, along with national anti-doping agencies and World Anti-Doping Agency, but did not comment further.

In December, Tuipulotu was named a chief of his family village in Samoa.

The Samoa Observer reported Tuipulotu as saying at the time: "I will be doing everything in my ability to help out my family with any problems they may face in the future."

ALL BLACK GREAT IN THE MAKING

Tuipulotu debuted for the All Blacks in June, 2014 after an outstanding debut Super Rugby season for the Blues. However, double hip surgery in 2015 meant the 1.98cm, 120kg forward missed the 2015 Rugby World Cup.

His development as a ball-carrying, tough-hitting tight forward suffered another setback in 2016 when his Super Rugby season was disrupted by a hand injury.

But he returned to the All Blacks in for the Rugby Championship and joined the team on their end of year tour and has racked up 12 tests despite still being only 24.

He signed a new four-year deal with NZ Rugby in April, 2016.