David Goffin, John Isner, Karen Khachanov, Eugenie Bouchard, Kristina Mladenovic and Kiki Bertens will also participate from their homes in the April 27-30 online competition that is expected to be broadcast live on TV and social media channels.
Khachanov said, "This initiative is interesting and it will bring back some competition in our sport. I'm looking forward to challenge my fellow players and show my skills to the tennis fans around the world.''
There will be €150,000 in prize money for each of the men's and women's events. The winners then decide how much they want to donate to tennis players who are having a hard time financially without any tournaments to play.
Another €50,000 will be donated to reduce the social impact of the pandemic.
Each draw is expected to have 16 players competing.
The Madrid Open was one of more than 30 professional tournaments canceled or postponed because of the coronavirus pandemic. It had been scheduled for May 1-10.