Ernie Els did not work hard enough after undergoing major surgery on his left knee in 2005, according to world number one Tiger Woods.
South African Els was once riding high in the rankings but is now down in 20th place, having gone 41 tournaments without a victory.
"Ernie is not a big worker physically and that's one of the things you have to do with an ACL (anterior cruciate ligament) injury," said Woods, who had almost identical knee surgery last year.
"I feel pretty good with what I've done and I think Ernie could have worked a little bit harder," the American told reporters on the eve of the Deutsche Bank Championship, the second tournament of the PGA Tour's four-event FedExCup playoff series.
It has been nearly three years since Els spoke about a three-year plan to challenge Woods for the number one spot.
The triple major winner has, instead, gone in the opposite direction in the rankings although he has shown encouraging form of late.
Els was joint eighth at the British Open in July and equal sixth at last month's US PGA Championship before finishing one shot behind winner Heath Slocum at last week's FedExCup opener, the Barclays Classic in New York.
With his 40th birthday approaching on October 17, the South African understands he no longer has time on his side.
"If I keep playing the way I did last week, maybe the three-year plan can be revived," Els said. "I feel positive and feel my game is coming around so I just want to try and win.
"I got a win early last year and then I really didn't hit form at all so it's been an awkward couple of years.
"I don't want to be struggling like I did. There's no worse feeling than to play at a certain level and then drop off, knowing you can do a lot better," added Els.
The 1994 and 1997 US Open champion and winner of the 2002 British Open said he was down in the dumps a few months ago.
"I hit my low point at the US Open (in June)," said Els, referring to his missed cut at Bethpage Black.
"I just want to get back to where I feel I should be, that's top five in the world at least and winning tournaments."
