The Manchester City defender was included in Alejandro Sabella's party announced on Tuesday, but admitted he was mildly shocked to have been chosen after featuring in just two of his country's qualifying matches.
The former Bayern Munich and River Plate defender played 27 Premier League games this season as City regained their top-flight crown.
"I felt that I was out of the national team," the 33-year-old told America and Closs.
"I didn't imagine that I was going to be talking about a recall to the team. This season has ended in the best way for me after we won the Premier League.
"My recall was a surprise, but with a big desire. I think that I am in a great moment.
"I was asked several times if I still thought I could be recalled and I always answered that while I am physically well, I had the wish.
"Now that I have the chance that I wasn't really expecting I am going to try to fight for a place and take advantage of this opportunity."
Demichelis has 37 caps for his country and will hope to make the cut when Sabella names his final 23-man squad at the beginning of June.