The seven-year-old show, which stars Sarah Michelle Gellar, has suffered from poor ratings since it moved channels in 2001, from the WB network to UPN.

CBS chief Leslie Moonves, who is responsible for UPN, said the future for writer and producer Joss Whedon's show was uncertain, according to the Hollywood Reporter.

"I wouldn't bet that it comes back, but it's possible," said Mr Moonves.

He said several options were being discussed for the future of the show, which is now in its seventh series, including a spin-off.

Decision

There has already been one spin-off, Angel, but that has stayed on the WB network.

Mr Moonves said Buffy star Gellar had yet to make a decision on whether she wanted to quit her role as the Californian vampire slayer.

It is widely thought she will leave the show to concentrate on a career in the movies.

She has already starred in the live action film Scooby-Doo, alongside husband Freddie Prinze Jr, and Cruel Intentions.

Mr Moonves stressed that no more money would be made available for the show, with UPN already splashing out more than $2.4m (£1.4m) per episode.

UPN - which stands for United Paramount Network - poached the show from Warner Bros-run WB in order to boost viewers for the struggling cable network.

The youth-orientated channel continues to lose money for its parent company Viacom but bosses are confident the channel is "turning the corner", partly thanks to its coverage of WWE wrestling.

Buffy is shown on Sky One and BBC Two in the UK, while Angel is screened by Sky One and Channel 4.