The Norwegian was forced off during City's FA Cup quarter-final clash with Bournemouth over the weekend.
Moments after failing to convert a penalty-kick, Haaland was on the floor and in need of treatment for a suspected ankle injury.
He was replaced by January signing Omar Marmoush, who would go on to score the match-winning goal.
Haaland has had initial tests and is now expected to miss 'most of the final part of the season', as originally reported by Italian journalist Fabrizio Romano.
The striker will now seek specialist consultation, with hopes that he could play again before the end of the season.
City could very well have an FA Cup final to play in, if they're able to beat Nottingham Forest, and will be in action at the Club World Cup over the summer.
"Erling underwent initial tests in Manchester on Monday morning and will now seek specialist consultation to confirm the full extent of the injury," a statement by City said.
"Assessment remains ongoing to ascertain a full prognosis. The expectation is that Erling will be fit in time to play a further part in the remainder of this season, including this summer’s FIFA Club World Cup."
Man City are next in action against Leicester this coming Wednesday, but Haaland obviously won't be available.
Pep Guardiola's men will face Forest in the FA Cup semi-finals on Saturday, April 26th. The final will be played on May 17th.
The Club World Cup will get underway for Man City on June 18th, when they'll face Morocco's Wydad Athletic, which could be a realistic target for Haaland.