After making racist comments about 23-time grand slam champion Serena Williams, Romanian tennis captain Ilie Nastase is under investigation by the International Tennis Federation (ITF).

Speaking at a press conference at the London Fed Cup on Friday, the 70-year-old referenced Williams’ recently announced pregnancy and was heard saying in Romanian, “Let’s see what colour it has. Chocolate with milk?”

35-year-old Williams announced she and fiance Alexis Ohanian were expecting their first child together on Wednesday, posting a selfie of her growing baby bump that read, "20 weeks."

Following the damning comments, Nastase - who was at one point in the 1970s ranked World #1 - denied any racism, saying it was simply a joke that the media had misunderstood.

“This was a joke,” he told Romanian news channel Digi24.

Listen: Serena Williams is not here to make friends or please people. Post continues... 

“If someone didn’t understand it, they lack humour. They have their own humour and we have our humour,” he continued, adding he and Williams have a friendly relationship.

Nastase then took aim at Eleanor Crooks, the British Press Association journalist responsible for first reporting on the comments, asking her, “Why did you write that? You’re stupid, you’re stupid.”

According to Crooks, Nastase also "asked me why what he said was racist."

Hours later, Nastase was then removed from the Romania vs the UK match for swearing at the umpire, “What’s your f**king problem?” and calling British players Anne Keothavong and Johanna Konta “f**king b**ches.”

The comment toward Keothavong came a day after Nastase had asked the UK player for her hotel room number at an event on Thursday evening and again on Friday morning in front of the media.

Announcing its investigation into Nastase's behaviour on Saturday, International Tennis Federation president David Haggerty released a statement that called the former player's courtside behaviour “unacceptable."

“The ITF does not tolerate discriminatory and offensive language and behaviour of any kind," a press release from Haggarty read.

“We are aware of alleged comments made by Romanian captain Ilie Nastase and have begun an immediate investigation so that we have the full facts of the situation before taking further and appropriate action.”

Serena Williams has not responded to the comments.