The Highlanders play the Sharks at Forsyth Barr Stadium, wanting to get a win after a painful eight straight losses to start the season.
Ellison has been out all season after a shoulder operation at Christmas, and was not expected back until June at the earliest.
But he has been working hard on his rehabilitation programme and has been training with the side at full contact for the past few weeks.
Coach Jamie Joseph said Ellison appeared fine to play and would be an asset for the Highlanders.
''Tamati Ellison is a quality footballer but he has had nearly six months off so it is not going to be easy for him to come straight back in and perform,'' Joseph said.
''But in saying that, he is an experienced guy who brings a lot of confidence to those younger guys around him.''
Ellison will likely slot in at centre, outside Ma'a Nonu, although the All Black second five-eighth had a minor operation to his face last week to remove a growth. He is expected to be right for Saturday.
The Highlanders had the bye last weekend, bagging four points in the process, and the players had the whole week off before coming back together yesterday to start preparing for this Saturday's match.
''We are looking at these next five games that we play as a sort of mini-season,'' Joseph said.
''They are all going to be played on hard, firm tracks so we will be looking to play some running rugby.''
They return to Dunedin on June 1 to play the Blues. The South African and New Zealand sides then have three weeks off for the June internationals.
With the Highlanders - widely tipped to make the playoffs before the season started - at the bottom of the table, Joseph said the emphasis was to just concentrate on the game on the field and not get too complicated for the rest of the season.
The players had enjoyed a week away and had trained well yesterday.
''We just need to look at simplifying things and get a fresh start for everyone. I thought in our last match against the Crusaders we did some good things and were not far away.''
The set piece was disappointing in Christchurch, as the Crusaders won 24-8, and Joseph said that was obviously something that needed to be addressed.
Ellison may be back but there is a shortage outside him, with both Kade Poki and Buxton Popoali'i unlikely to front on Saturday.
Poki is still nursing sore ribs while Popoali'i is struggling with a foot injury and, if rest does not fix the injury, he may be forced to have an operation, which will end his season.
Declan O'Donnell did not front for the season at all, being wiped out with a shoulder injury in January.
Tony Ensor made his Super 15 debut on the wing in the match against the Crusaders but is lacking experience. The option may be to move someone like young centre Jason Emery to the wing if Ellison starts.
Joseph said he was looking at Otago outside backs as replacements but Matt Faddes had played little rugby of late, while Jayden Spence was more of a midfielder.
Key Sharks back Francois Steyn has been given approval to play on Saturday night after being cleared of making an illegal hit.
Steyn appeared at a judicial hearing last night via video conference after being cited for an alleged illegal entry to a ruck late in Saturday night's game against the Chiefs.
But video evidence presented at the hearing and the fact no penalty was given at the time of the incident led to Steyn being cleared of the charge.
