"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 number one ranking to Australian Jason Day earlier this week.
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The American has also done a lot of golfing globetrotting this year and Strange, who won the U.S. 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 learnt from it," said the 2001 U.S. Ryder Cup captain.
"He learnt 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 who will be commentating at the Masters (see www.espn.co.uk for coverage details).
"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."
(Editing by Ken Ferris)
