Greengrass's Bourne ultimatum

In a career spanning eight books and three action movies, Jason Bourne has survived attempts on his life by drug barons, the CIA, Russian gangsters, and security forces representing half of Nato. Now he must face a fresh threat: a British film director with itchy feet.

The future of the rogue secret agent, who is at the centre of one of Hollywood's most valuable film franchises, was cast into confusion yesterday, after Paul Greengrass announced that he was quitting the blockbuster series, in circumstances that remain unclear.

Greengrass directed 2004's Bourne Supremacy and 2007's Bourne Ultimatum, which were critically acclaimed and made a combined total of more than $700m (£440m) at the box office. But he has abruptly removed himself from the helm of the still-unnamed "Bourne 4", which was to begin filming next year.

As rumour and counter-rumour crossed Hollywood, it also emerged that Matt Damon, who plays Jason Bourne and is the "face" of the billion-dollar franchise had not yet signed a contract to appear in the film, either.

In a statement from Greengrass, released by Universal Pictures, the studio backing the project, the director denied reports of an artistic dispute, saying he had decided to withdraw in order to seek "a different challenge".

"My decision to not return a third time as director is simply about feeling the call for a different challenge," it read. "There's been no disagreement with Universal Pictures. The opportunity to work with the Bourne family again is a difficult thing to pass up, but we have discussed this together and they have been incredibly understanding and supportive."

"I've been lucky enough to have made four films for Universal, and our relationship continues. Jason Bourne existed before me and will continue, and I hope to remain involved in some capacity as the series moves on."

A different story was playing in the blogosphere, however. The Playlist, a film industry website that broke the news of the director's departure, claimed Greengrass was leaving after a row over a decision by Universal to hire a screenwriter called Josh Zetumer to write a "parallel script" for the film.

The move upset the director, claimed the website, because it had been forced upon him. Greengrass had allegedly preferred an initial screenplay prepared by George Nolfi, a writer he admires, and who also boasts a close relationship with Damon.

Sources at Universal strongly disputed that version of events, and denied reports that Greengrass is in conflict with studio executives over the cost of Green Zone, a film about the Iraq War also starring Damon, which has already reached $100m (£62.5m) – a significant sum given that films about Iraq tend to perform poorly at the box office.

The studio has experienced a difficult year, with a string of expensive flops such as the Will Ferrell vehicle Land of the Lost, and the news could barely have come at a worse time for the future of one of its most profitable franchises to be called into question.

It is rare for a director so publicly attached to a blockbuster to leave so suddenly without a successor being named and, in the absence of Greengrass, the project, which was scheduled for release in 2011, may now be pushed back.

The leading contender to fill the director's chair is Doug Liman, who directed the original 2002 film The Bourne Identity, and whose presence Universal must hope would entice Damon to remain involved.

Provided they can survive this setback, Universal has plenty of material to allow them to carry on churning out Bourne films, which are based on a trilogy of novels by Robert Ludlum, who died in 2001. Since then, no fewer than four subsequent books have been ghost-written and released. A fifth, The Bourne Objective, comes out next year.