Iniesta, who scored the extra-time winner for Spain in the World Cup final against Holland on Sunday, struggled for long periods last season with a thigh problem and only reappeared for Barcelona right at the end of the campaign.
The midfielder then aggravated the injury in Spain's friendly win over Poland before the start of the World Cup and was forced off once more as Del Bosque's side went down 1-0 to Switzerland in their opening match in South Africa.
But the 26 year-old returned to play a key part in Spain's first ever World Cup success and scored the crucial goal four minutes from the end of extra time on Sunday.
"I have always had faith and confidence. I had a lot of confidence in this team from the very first moment." he said in a press conference organised by Nike in Barcelona on Tuesday.
"It has been a difficult season, hard for me in many ways, but there have also been moments of the season when I have felt good. It has simply been a hard season and nothing more.
"Then there was the World Cup and all of us were so excited and keen to play. I really hoped things would turn out well for me and after the first game, everything changed - the team recovered well and it ended up as we know it could."