Christie Brinkley thinks Serena Williams is ''over-the-top amazing''.

The 35-year-old professional tennis player - who is expecting her first child with fiancé Alexis Ohanian - is currently gracing the cover of Vanity Fair magazine where she shows off her burgeoning baby bump wearing nothing but a thong, and model Christie has nothing but high praise for the star.

Asked if she could put Serena on a scale from one to 10 based on her cover shoot, Christie said: ''Gorgeous. She's an 11. She's off the scale. She is over-the-top amazing.''

And the 63-year-old model - who has daughter Alexa, 31, from her marriage to musician Billy Joel, son Jack, 22, with third husband Richard Taubman, and daughter Sailor, 18, with her fourth husband Peter Cook - dubbed the tennis champion as ''the epitome of success'', as she claimed she is both ''beautiful and strong''.

She added: ''I think it's wonderful. I think that she is the epitome of success on every level. You know, she's the greatest tennis player to ever play, and she's beautiful, strong, and a mother-to-be. I mean that's everything.''

Christie was also asked whether she would want to appear on a magazine cover alongside Serena.

She told TMZ.com: ''Are you kidding me? It would be an honour.''

Meanwhile, Serena recently revealed she has done ''nothing'' to prepare for the impending arrival of her child, as she admitted she ''doesn't know what to do'' with a baby.

She said: ''It just doesn't seem real. I don't know why. Am I having a baby?

''If you would have told me last year in October or November that I would have a baby, not be pregnant but have a baby, I would have thought you were the biggest liar in the world.

''This is kind of how I am right now. This is happening sooner than later, and it's going by so fast. I don't know what to do with a baby. I have nothing ... I've done absolutely nothing for the baby room.''