The fourth instalment of the animated series, Shrek Forever After, is currently in UK cinemas and is said to be the 'final chapter'.
However, the actors, who voice Princess Fiona and Shrek in the movies, said that they remained hopeful for the characters' future.
"We're the last people to know anything that's going on, is the absolute truth. I don't know what's to be with the series," Myers told Empire.
Diaz added: "I'm hoping it's just a big Hollywood joke, that they're pretending that we're not going to make another movie and then we're back!"
Shrek Forever After recently topped the UK box office, knocking Get Him To The Greek off the top spot.