The Catalan giants spent £15.9m to acquire the French centre-back from Valencia last month as a replacement for now-deaprted Carles Puyol.
However, some fans have been critical about signing a 30-year-old for such a high figure and the social media furore around Mathieu smoking has not helped his antagonists warm to him, but he has now stressed that he hopes he can be judged on the pitch rather than for his personal choices off it.
"I do not smoke much but I do smoke when I want," Mathieu is quoted by Marca as saying on Friday. "It is a personal thing.
"What actually matters is what happens on the field and people forget that I go running. I want the best for the team, above my own personal goals."
Barcelona are unlikely to be pleased with Mathieu's attitude towards smoking. Last year they partnered with the European Commission to launch an anti-smoking campaign and Camp Nou is now a smoke-free stadium.
Spanish regional newspaper Superdeporte claims that Valencia repeatedly attempted to address Mathieu's smoking habit - even allegedly speaking to the defender's wife - but their efforts were in vain, suggesting that Barca may have just as little success if they try to talk him out of it.