Usain Bolt was stunned to learn he must take a drugs test despite having retired from athletics and waiting to learn if he will be given a professional contract in football.

The former sprinting star took to Instagram on Monday to show a testing notice he has received, apparently from Football Federation Australia (FFA).

"So guys, I've retired from track and field looking to become a footballer but look at this," said Bolt, before showing the letter on the video.

"How am I going to get a drug test today? I'm not even a professional footballer yet. Seriously.

"So I asked the lady: 'Why am I getting drug tested when I haven't signed for a club yet?' and she said they told her I'm an elite athlete so I have to get tested. Okay then."

Bolt is on trial with A-League side Central Coast Mariners, who are yet to offer him a contract.

The 32-year-old, who holds eight Olympic gold medals and the world records in the 100 and 200 metres, scored twice in a pre-season friendly last Friday.