The diagnosis, which also sees Owusu suffering with pneumonia, was confirmed by club doctor James Ilic after the Ghanaian striker started feeling flu-like symptoms just under a week ago.

It is unknown exactly where and when Owusu contracted the virus, but Dr Ilic believes it is likely to have happened either shortly after he touched down in Australia or on the flight over from England.

"Lloyd has got confirmed swine flu complicated by pneumonia. You can get varying side effects such as aches with the virus but Lloyd got pneumonia with it," Dr Ilic said.

"The incubation period would suggest that he either got it almost straight after arriving in Australia or on the flight from the UK, they're the two likely scenarios."

Having arrived in Adelaide on June 30, the 32 year old had been training and working on his conditioning in order to be ready for United's round one match against Perth Glory on August 7, but now it is unlikely he will be available for the Reds' season opener.

"He has been in isolation since Sunday. He's progressing well but he's still awhile away from joining the main group," Dr Ilic said.

"It's no different from dealing with human influenza, which is relatively common. It's just a matter of him getting plenty of rest, symptomatic treatment and lots of fluid, and treatment with the anti viral drug Tamiflu."

Owusu was hoping to get himself into peak condition in order to make an immediate impact for the Reds, but this setback has given him a less than ideal start to his career in Australia.

"Definitely it's a massive setback but at the end of the day health is the most important first and foremost," Owusu said.

"I've never had this before so it was like ‘welcome to Adelaide, thanks very much'. I'm slowly getting my energy back and I feel a lot better but internally the pneumonia is still there.

"I'll just get back in with the boys slowly but we just need to make sure we manage it well, but to be fair I realistically probably won't be in action for a week or two yet."