Roy Keane fired a sly dig at Manchester City's perilous title charge following Saturday's 2-1 derby defeat to Manchester United at the Etihad.
Goals from Marcus Rashford and Anthony Martial in an excellent opening 30 minutes for the Red Devils condemned Pep Guardiola's side to their fourth Premier League defeat of the season.
The result leaves City's hopes of claiming a third successive title hanging by a threat, with the champions now 14 points behind leaders Liverpool.
Speaking on Sky Sports News after the game, Keane said: "To win the league championship, you've got to go and earn it.
"For City, they've won it for the last couple of years - fantastic - but we all know how difficult it is to win three years in a row. Not many teams do that."
The former United captain was alluding to the fact that his former club remains the last team to win the Premier League three times in a row between 2006 and 2009.
