People pass by a closed movie theater on April 09, 2020 in New York City.

With theaters closed for the foreseeable future and studios postponing blockbusters until 2021, this year's box office is expected to fall more than 40% compared with last year, a new report predicts.

Wedbush analyst Michael Pachter said he estimates the 2020 box office will reach around $6.6 billion. The last time the box office was this low was in 1998, when the industry reported $6.7 billion in ticket sales.

Through the first three months of the year, sales at the box office have tallied $1.79 billion, a 25.4% fall from the same period a year ago.

"Our estimates reflect our opinion that most theaters will remain closed domestically well into June, with a slow recovery over the balance of the year," Pachter wrote in a note Monday. "We expect some regions to remain closed for several months."

Social distancing restrictions across the U.S. forced theaters to shutter and studios to shuffle their slate of films for 2020 and beyond.

Disney has moved "Mulan," which was displaced in March, to July 24. That spot was held by "Jungle Cruise," which will now arrive a year later, in July 2021.

"Black Widow" is now set for Nov. 6, the date previously held by "Eternals." All of the Marvel Cinematic Universe movies have now been shifted as a result of this change.

Sony has delayed most of its 2020 features to be released next year — "Morbius," "Ghostbusters: Afterlife," "Uncharted" and "Peter Rabbit 2″ — and Universal pushed "Minions: The Rise of Gru" to 2021 alongside "F9."

There are currently 17 films that have been pulled from the box office schedule that do not yet have a new date, Pachter noted.

On Monday, shares of Marcus Corporation, the owner of Marcus Theaters, were down more than 5%, Cinemark shares are down more than 8% and AMC, which is reportedly in talks to hire bankruptcy lawyers, saw shares plummet 17%.

AMC shares have lost more than 70% of their value since the start of the year.

Disclosure: Comcast is the parent company of CNBC and NBCUniversal.