Definition from Wiktionary, the free dictionary
have a mountain to climb
- (idiomatic) To be faced with a difficult task or challenge.
2011 October 1, Phil Dawkes, “Sunderland 2 - 2 West Brom”, BBC Sport:
- The Black Cats had a mountain to climb after James Morrison's header and Shane Long's neat side-foot finish gave Albion a 2-0 lead five minutes in.