Otamendi left Manchester City for Benfica last summer after spending five years at the club and winning two Premier League titles with the Premier League giants.
Manuel Pellegrini signed the Argentine in 2015, but he played some of his best football under Guardiola and won both Premier League titles under him.
He admits that he feels lucky that he got an opportunity to work under Guardiola and believes the Manchester City manager made him improve and become a better footballer.
The 33-year-old stressed that the Spaniard provided his players with all the tools necessary to improve themselves and admits that in each training session he learned something more and new about the game under Guardiola.
Otamendi told The Athletic: “There’s nothing better than having a coach like Pep. Honestly, I was lucky to spend those four years with him.
“Yes, I do [think he made me a better player].
“Pep gives you all the tools you need to learn; after that, it’s up to you to evolve. You have to concentrate.
“Honestly, the years I spent with him were very happy ones. I learnt something every day, in every training session, from every little tip.
“I’m fortunate to have had a coach like him.”
Guardiola’s Manchester City are on course to win their third league title in four years and are currently ten points clear at the top of the standings.