Novak Djokovic to become a father

Novak Djokovic and Jelena Ristic are going to be parents. (Robin Marchant/WireImage)

Roger Federer isn't the only member of the Big Four who's expanding his family. Novak Djokovic tweeted that his fiancée, Jelena Ristic, is also expecting a child.

There's no word yet on the sex of the baby or the due date. The couple dated for eight years before getting engaged last September.

Djokovic won the BNP Paribas Open and Sony Open in March. He's currently taking some time off to heal a wrist injury that flared up in Monte Carlo, but expects to be ready for tournaments in Madrid and Rome.