Buffy star yet to sign for second sequel.

Although Scooby Doo 2: Monsters Unleashed looks set to improve upon the original movie, the future of the franchise may be in doubt.

Stars Matthew Lillard (Shaggy) and Linda Cardellini (Velma) have both signed for a possible Scooby Doo 3. However, Sarah Michelle Gellar (Daphne) and hubby Freddie Prinze Jnr (Fred) have yet to put their names on the dotted line.

Speaking to the Sc-Fi Wire website, Scooby Doo 2 Producer Charles Roven explained further: "At the time that we started to make the deals for Scooby 2, even if you're not guaranteeing there's going to be a Scooby 3, you're going to want to talk about it.

"Matthew and Linda were very, very enthusiastic about where their characters had come from and where they were going and felt more positive about seeing out that far into the future and being able to say, 'Hey, you know what? We don't care what we're going to be doing. We're ready to go.'

"I think Freddie and Sarah were a little bit more cautious about that."

Roven went on to explain that Gellar had just finished up a seven year stint on Buffy when she jumped straight into production on Scooby Doo 2. "I think she just wanted to be a little more cautious about making a longer-term commitment out into the future," he said.

Scooby Doo 2: Monsters Unleashed goes on general cinema release in the UK on Friday April 2nd.