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The 23-year-old signed with the Stags in 2018 and impressed in his first stint with the side.
He re-signed for a further two years. But that contract is up and he has not recommitted for this season.
Asked what his plans were, Nu’u said he was doing some building work in Dunedin and some study on the side.
"I’ve just had a wee break and probably in the next week or so I’ll make a decision," he said
"I don’t think I could play for Otago. I’m pretty loyal to Southland because they took me in."
Dale MacLeod has previously indicated he would be happy for Nu’u to return.
But with Matt Whaanga joining the Stags this season, there is extra competition for a starting spot.
And MacLeod rates Whaanga highly.
Nu’u had a good battle with Harbour second-five eighth Willie Tufui at the weekend.
The sides had a 20-20 draw at Miller Park.
Nu’u went off early in the second half with blurred vision.
But he made some lovely touches in the opening 40 minutes, including a deft offload which created a scoring opportunity.
His side trailed 20-10 with about 10 minutes remaining but rallied to snatch a draw.
"We showed character and that was a good learning for us. We made a lot of errors but we stuck to our system."
Green Island has been one of the big improvers this season. The Grizzlies missed the six-team playoffs last season but are undefeated after four games this year.
The gutsy win against Taieri last month was perhaps a sign Green Island will be more of a force this season.
Rugby Southland has named its high-performance squad for 2021.
The squad is a made up of players who have signed with the Stags and players noted to be of potential.
The squad will assemble and train over the next several months. Contracts will be offered to selected players before the national provincial championship season, which kicks off in early August.
Forwards: Joe Walsh, Kane Prentice, Sanasco Crichton, Chris Barrett, Niko Manaena, Greg Pleasants-Tate, Flynn Thomas, Jacob Payne, Talemaitoga Tuapati, Caleb Aperahama, Joe Robins, Aleki Saili, Craig Smith, Ben Fotheringham, Ben Paulin, Matt James, Jacob Coghlan, Hayden Michaels, Dustin Coveney, Charles Alaimalo, Liam Udy-Johns, Arese Poliko.
Backs: Jay Renton, Liam Howley, Marty McKenzie, Greg Dyer, Bram Fodie, Emeka IIogu, Tevita Latu, Desmond Spooner, Matt Whaanga, Isaac Te Tamaki, Micaiah Johnston-Brown, Materua Tupou, Will Murray, Kieran Lee, Brad Kooman.