Notorious former tennis star Ilie Nastase is back in hot water after apparently making a racist comment about Serena Williams' pregnancy.

The International Tennis Federation (ITF) has confirmed it has launched an investigation into the comments by the Romanian captain on the eve of the country's Fed Cup tennis play-off against Great Britain.

At a press conference to preview the tie in Constanta, which starts on Saturday, Nastase was heard to say of Williams' unborn baby: "Let's see what colour it has. Chocolate with milk?"

The American world No.2 announced on Wednesday she will take time away from the tour as she is expecting her first child with fiance Alexis Ohanian, co-founder of the social news website Reddit.