Earlier this month Toulon owner Mourad Boudjellal revealed he wasn't too impressed with Nonu and fellow off-season signings Quade Cooper and Tom Taylor.
The controversial owner told reporters that Nonu was not yet a "lost bet" but had produced some "disappointing" performances for the club.
That was before Nonu set up a match-winning try against Wasps in the European Champions Cup.
Nonu said there was pressure on the overseas signings in the squad and admitted his play has been 'average' so far.
"It's a different sort of mentality here in France. There's lot of onus on the foreigners but we get over that," Nonu said.
"That's why I play rugby, because I enjoy the challenge. But sometimes I question myself why I enjoy this game, sometimes being over here because it's so frustrating at times.
"We won five games but I'm sure half are not happy and half are happy. I can't speak for the team, I can only speak for myself but I'm not happy with my performances, they're pretty average at the moment."
Toulon currently sit fourth on the Top 14 table, two points behind Dan Carter's Racing 92 side. They face 11th placed Stade Francais this weekend with Nonu looking to break his try-scoring drought in the Top 14.