The prolific attacker netted in his 17th consecutive Liga game at the weekend as the Blaugrana beat Deportivo La Coruna, but was unable to lead the way in the crucial matches versus AC Milan and Real Madrid.
"I think Lionel's the same as before on a day-to-day basis; I think he's fine. But I'm no hypocrite; I don't dress things up. It's obvious that he's been lacking some spark in recent games," the Brazilian told El Mundo Deportivo.
He added, "Why? I don't know. I haven't tried to find out. I only want to know what people want to tell me. And if someone doesn't want to talk about their life or what they're going through, then who am I to ask? I respect his privacy. But I've noticed that his head has been down a bit more than usual. I think what sets him apart from the rest is that he has a lot of character and when he gets it wrong, he keeps trying."
Barcelona is currently preparing for the second leg of its Champions League round of 16 tie against Milan on Tuesday, having lost the first leg at San Siro 2-0 back in February.