Cutting Joe Hart out of his first-team plans at Manchester City is the toughest decision Pep Guardiola has made at the Etihad Stadium.

Hart will miss out the 2018 World Cup after being left out of Gareth Southgate's 23-man party for the Russian tournament, which was announced on Wednesday.

It marks a stunning fall from grace for the two-time Premier League champion, who has been the Three Lions' starting goalkeeper in each of their past three major tournaments and was also first choice during the most-recent qualification campaign.

Guardiola placed Hart behind Willy Caballero in the pecking order at City and then signed Claudio Bravo in August 2016 amid doubts the Englishman could adapt to his demands of building play from the back.

An error-strewn season on loan at Torino in Serie A followed, before a similarly underwhelming temporary stint at West Ham, where losing the gloves to Adrian on two occasions due to poor form has seemingly played a decisive part in Southgate's decision.

Nevertheless, Guardiola recognises the important role Hart played at a club he has taken to new heights this term.

"It's always difficult because they are human beings and had been together years and had a good relationship, but we had to do it," he told Sky Sports.

"People ask me about the toughest decision and it's Joe Hart. Because I know how professional he is and how important he is for the club and what he has done.

"I am at the club like I am because of people like Joe. But you have to do it, because we believe it is the best and you have to take the decisions, that's our job."

Hart, 31 and with 75 England caps to his name, has one year remaining on his contract at City.