Cowan, who will celebrate his 27th birthday on Friday, has had a frustrating start to the season, spraining his right elbow just 16 minutes into the side's first match against the Brumbies, knocking him out of the next two games.
But coach Glenn Moore said Cowan was almost certain to be available.
His injury simply needed rest and he had recovered well over the past week.
The All Black halfback's return will be a big boost for the Highlanders, as the side's lack of experience was shown up at vital times in the past couple of weeks.
His replacement, Sean Romans, has played well, his kicking game being particularly impressive.
Lock Tom Donnelly may also be available although his fitness and readiness for the game will be assessed in the next couple of days.
Donnelly ruptured a ligament in his thumb during a tackling practice in pre-season and has not played any rugby in 2009.
Moore said Donnelly's fitness was good as he had done plenty of running but it was just whether he could stand up to the rigours of contact play.
Josh Bekhuis and Hayden Triggs had locked the scrum in the first three games, and had been playing well, so that would have to be taken into consideration if Donnelly was available, Moore said.
Donnelly had been a key player in the Highlanders line-out in the past few years and his aerial skills would be a big asset for the Highlanders.
Prop Clint Newland left the field in the 34-16 loss to the Waratahs last Friday but Moore said he was fine and should be available for Saturday night.
Moore said the game in Sydney came down to a few critical errors at vital times.
"We gave them opportunities to be in games and threw too many of those 50-50 passes which lead to knock-ons," he said.
"It was stuff we'd not been doing.
At the end of the day we've got to be more patient and just suck the ball in and wait for the opportunity to come about."
He said the side just needed a win, which would help immensely with confidence.
"We just need to get one across the line and that is why it is disappointing we didn't win one of those first two games."
He said spirits in the team were high and there was excitement looking forward to Saturday night's match.
He hoped for a good crowd to get in behind his side, as the team starts a run of five home matches, although they are spread among Dunedin, Invercargill and Palmerston North.
The side had a short training session at Balmacewen Intermediate School yesterday morning.
