Pep Guardiola has said building a new team at Manchester City isn’t the “biggest challenge” of his career. Guardiola has won 18 trophies, including six Premier League titles and a Champions League, since joining City in 2016. However, the club have endured a spectacular fall this season. They are fourth in the Premier League, 20 points behind leaders Liverpool, and have endured early exits in the Carabao Cup and Champions…