The 33-year-old spent three years at Camp Nou before departing for Sporting in the summer, at which point he came in for criticism from technical director Robert Fernandez and president Josep Maria Bartomeu.
Mathieu was also unhappy with comments made by Catalan daily Sport in the wake of Barca's defeat to Juventus in the Champions League last season, hinting that he will make his feelings known should his new side pull off an upset on Wednesday night.
"I don't know [if I would celebrate]," he told reporters. "I have a lot of respect for my former teammates and the fans. If I celebrate it will be for Bartomeu and Robert Fernandez, because I think the way they treated me was very difficult for me.
"It was just the two of them. But that's football and now I'm very happy. I do not care anymore. With respect to Barcelona itself, here I feel a bit like when I was in Valencia. It is a very familiar club and I was comfortable from day one.
"The newspaper Sport, I'm a little fucked [off] with them because every time I played they always had something bad to say against me. Football is a team sport and when you lose it is never the fault of one, that is my opinion. I have seen the match against Juventus and everyone says that I was the problem.
"It is true that [on the first] goal I am one against one and do not tackle, stand off and then they make a pass. They could say 'what does [Javier] Mascherano or [Gerard] Pique do?', but no. It is my opinion."
Mathieu has made a strong early impression at the Estadio Jose Alvalade, netting a fine free kick in the recent 2-0 win against Tondela.