Alton Towers owner Merlin Entertainments says the rollercoaster accident in June at the theme park has significantly reduced visitor numbers.
Since the beginning of the year, it has reported a 11.4% drop in revenue compared with last year at its Resort Theme Parks.
These include Alton Towers, Chessington World of Adventure and Thorpe Park.
Alton Towers was temporarily closed after 16 people were injured in a collision on the Smiler rollercoaster.
Based on trading during the summer, as well as future bookings, it expects profits for 2015 to be at the lower end of between £40m and £50m in its theme parks division.
This compares with profits of £87m last year.
Immediately after the accident, Merlin also suspended advertising for its theme parks and temporarily closed rides at other sites.
Merlin said the disruption could continue to affect the profitability of its theme park group in 2016.
Nick Varney, the chief executive of Merlin Entertainments, said: "The trends we reported at the half-year have continued throughout the summer.
"The performance of our Legoland Parks Operating Group has remained strong, with very positive guest satisfaction.
However, this has been offset by the impact of reduced visitation across the Resort Theme Parks Operating Group, primarily at Alton Towers resort, and euro weakness impacting visitation at our London attractions."
The accident on the Smiler rollercoaster happened on 2 June when it collided with an empty carriage that had come to a halt on the track.
Leah Washington, 17, had a leg amputated following the accident, while her boyfriend Joe Pugh, 18, suffered severe knee injuries.
Vicky Balch, 20, also had a leg amputated, while Daniel Thorpe, 27, suffered a broken leg and a punctured lung.
Merlin Entertainments' share price dropped more than 1% in early trading.