French supporters and media have rounded on the 32-year-old French captain in recent months over his perceived lack of form and have called for him to be dropped.
"We need him," the Barcelona coach said. "Without him we would never have got six titles (in 2009) and without him it will be harder this year.
Henry played a key role in the Spanish giants' La Liga and Champions League victories last year, bagging a total of 25 goals in all competitions. But the Frenchman has scored just three goals so far this season as Barca's young guns such as 22-year-old Pedro stake a claim for his place in the starting XI.
"If he does not play it is, among other things, because maybe there are players in better form than him," Guardiola told the club's official website. "He is conscious that he has to improve and I think that he knows what he is doing. I want him to have the same desire that he has always had. I am sure that he will be back to his best in the next couple of months," the 39-year-old coach added.
"It surprises me that some people say the deserves to be in the reserves for the France World Cup Squad. He is always an example for us in the dressing room. On the pitch, his behaviour has been exemplary," he said.