Dellas, who played 53 times for Greece and lifted the Euro 2004 title, watched on as Ranieri struggled during his tenure with Greece in 2014 - failing to win a single game.
Ranieri recorded one draw and three defeats – including a 2-1 reverse against the Faroe Islands – as Greece failed to qualify for Euro 2016, but has enjoyed remarkable success at Leicester this season.
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His side have confounded the odds to lead the way with 12 games to go, although Sunday's last-gasp 2-1 defeat to Arsenal saw their advantage cut to two points.
"It is totally different to be a national manager than being a coach in a club," said Dellas. "You have the players available every day, working and teaching them your philosophy.
"Leicester's position is a big surprise. But I think that both successes, Leicester and Greece at Euro 2004, come through team work.
"Of course Leicester has world-class players, but also has a very, very good team."