It is an inflammatory joint disease which can cause stiffness, pain and lack of movement, but Mickelson said: “Everything is fine now.”
He was on anti-inflammatories during the Scottish Open and The Open last month – he missed the cut at Loch Lomond and was only 48th at St Andrews – but for the last two weeks has been injecting himself weekly with a drug that he has been told to take for the next year.
The problem started just before the US Open in June.
“I woke up and had intense pain in some joints and tendons, so much so that I couldn’t walk,” he added. “It progressively got worse, so I got it checked out.”