"The plan now is to return on his favoured clay surface in South America in February.
"His camp say he is suffering from a stomach bug, which is the official reason for pulling out. However, the knee has been a worry. This comeback was eagerly anticipated but the problems have not cleared completely.
"The hard courts in Australia in the heat hold a particularly damaging danger to lower joints and it seems this virus has come at the wrong time.
"Acapulco will now be the surprise scene for his return. With every setback though, one starts to wonder if that is a bit ambitious."
The injury forced the Spaniard, who has won 11 Grand Slam events, to withdraw from both
He also pulled out of an exhibition tournament in Abu Dhabi on 27 December.
"My knee is much better and the rehabilitation process has gone well, as predicted by the doctors, but this virus didn't allow me to practise this past week," Nadal said in a statement.
"Therefore I am sorry to announce that I will not play in Doha and the Australian Open, as we had initially scheduled."
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.