The Argentine was out with a knee injury for most of last season.
Heinze said: “That win (against Benfica) helped prove we are not in crisis as people said after we lost to Arsenal and drew with Reading.
“Benfica are difficult rivals, especially on their own ground, but we won and the journey back was one of the best I can remember.
“I’m happy with the way I’m playing, but I am still a long way off the maximum. There is a lot more to come.”