The 36-year-old singer, presenter and designer first rose to fame in the pop group after they were put together on reality show Popstars in 2001. They disbanded the following year, after releasing two albums and four singles, reported Digital Spy.
"I just think that at any given point, whatever happens, there will always be two members on rotation, who just can't do it," Klass said.
"I think at the moment it's a resounding no. But I have learnt to never say never."
The singer, who was in the group alongside Kym Marsh, Suzanne Shaw, Danny Foster and Noel Sullivan, added that she admires other acts who have managed to reunite and loves the "nostalgia".