Double US Open champion Curtis Strange believes Jordan Spieth may never repeat the scintillating form he showed in 2015 that sent him rocketing to number one in the world rankings.

Everything the young Texan touched seemed to turn to gold as he landed his first two major championship victories at the US Masters and US Open, and won the Tour Championship to sew up the lucrative end-of-season FedExCup Series.

"Last year was a phenomenal year for any player, much less for a 22-year-old," Strange said in a conference call ahead of Spieth's Masters title defence at Augusta National next week.

"It could turn out 20 years from now that could be his absolutely best stretch of his life. I don't think so, I hope not, but it very well could be.

"If he holds himself to the standard that he played for four or five months last year, it's going to be difficult to repeat day in and day out."

Spieth's consistent brilliance last year has given way in 2016 to a series of poor rounds and he lost the world No.1 ranking to Australian Jason Day earlier this week.

The American has also done a lot of golfing globetrotting this year and Strange, who won the US Open in 1988 and 1989, believes that has led to an inevitable downturn in fortunes.

"I think he did do a little bit too much (travelling) but... I think it was good that he did it this early in his career because he learned from it," said the 2001 US Ryder Cup captain.

"He learned that it does wear you out. I think he's probably a little tired.

"I sense he's just not making the putts that he made last year. There's nothing wrong with his game," added the 61-year-old Strange.

"He's probably a little bit impatient. The putts aren't going in but I think he's fine. He's going to be defending at Augusta next week, he'll get fired up," he said.