Tennis legend Ilie Nastase is under investigation by the International Tennis Federation for derogatory comments made about Serena Williams' unborn child.

According to ESPN, at the Fed Cup draw in Romania over the weekend, Nastase, the former world number one, was heard speaking to one of his former teammates about Serena's baby.

"Let's see what color it has. Chocolate with milk?"

Serena announced last week that she is expecting her first child with fiancee Alex Ohanian, and is currently 20 weeks pregnant.

The International Tennis Federation released the following statement regarding Nastase's remarks, noting that an immediate investigation has been launched.

"The ITF does not tolerate discriminatory and offensive language and behavior of any kind," the Federation said in an emailed statement.

"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."