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 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 said on the eve of the Deutsche Bank Championship, the second tournament of the PGA Tour's four-event FedEx Cup playoff series.
It has been nearly three years since Els spoke about a three-year plan to challenge Woods for the No. 1 spot.
The three-time major winner has, instead, gone in the opposite direction in the rankings, although he has shown encouraging form lately.
Els tied for eighth at the British Open in July and then tied for sixth at last month's U.S. PGA Championship before finishing one shot behind winner Heath Slocum at last week's FedEx Cup opener, the Barclays Classic in New York.