The pair will reprise their roles in Karen + Jack, which is currently in development at the NBC network.
According to American tabloid The National Enquirer, Hayes was keen on a spin-off soon after Will And Grace ended in 2006 - but was put off by the failure of Matt LeBlanc's Joey.
An unnamed insider said: ‘They feel there is still a lot of life left in their characters and a lot of comic possibilities.’
If a pilot episode is successful, Karen + Jack is likely to air in the US in autumn 2009.
