Fekitoa (24) will start for the Highlanders at second five-eighth tonight in the semifinal against the Lions.
A few quiet questions have emerged surrounding the All Black midfield back and whether he is playing at his top form.
There were a couple of handling errors last week against the Brumbies, although the wet weather did not help.
Joseph said Fekitoa came back from the All Black camp in June injured and was getting used to a new role.
In his first two years at the Highlanders he played all but four games for the Highlanders at centre and was a powerhouse in the midfield.
Fekitoa was still the same ball of muscle and was due to have a good game, Joseph said.
"He got injured with the All Blacks in June and then came back to us. He is a power athlete who is taking time to get used to his new position at 12,'' Joseph said.
"He has got there because of the skill and speed of Matt Faddes. He's coming to understand the position.
"But he is a big-game player. I think he is ready for a big game on Saturday.''
The big Tongan has not had as many metres as previously but defences are marking.
There are question marks whether Fekitoa and his power game is suited closer to the set piece at second five-eighth but it did not seem to have an impact on someone like Ma'a Nonu.
Fekitoa will have an added incentive to play well against the Lions tonight.
If the Highlanders make the final next week, Fekitoa will make his 50th appearance for the southern franchise.