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Masters favourite Phil Mickelson has played down fears that a back condition will hamper his attempts to defend the title at Augusta National this week.

Mickelson was diagnosed with psoriatic arthritis last summer and went to visit a back specialist on Monday to assess his fitness.

"I saw a specialist last night just to make sure that my back hangs in there. It feels terrific," said Mickelson.

"This week is the one week where I swing the absolute hardest."

Mickelson, 40, did not practise on Tuesday but dismissed suggestions it was to protect his back.

"I've been working on it for some time to make sure it's strong enough to withstand the type of rotational speed that I'm going to be trying to apply this week - because I believe it's a big advantage if you can move it out there," he said.

"My schedule has changed a little bit given the weather conditions and so forth.

"I'll end up playing a practice round tomorrow [Wednesday] instead of today [Tuesday] and try to play in conditions similar to what we'll see this weekend."

An overnight thunderstorm had brought down trees - including one on the famous Magnolia Lane drive up to the clubhouse - and had softened up the course.

But the forecast is for fine weather the rest of the week and for increasing temperatures.

Mickelson, who won the Houston Open on Sunday, will be back having two drivers in his bag, just as he did for his 2006 victory.

"Because it's going to be warm I won't need a three-iron or a hybrid, so the longest iron I'll have is a four-iron," he said.

"I'll put in a second driver that will allow me to carry the bunkers on one, two and eight.

"They both draw and fade the same. That's not the purpose of it - I have an inch longer shaft and different loft and it just goes about 15-20 yards farther."