Garnett was injured during a Feb. 19 game at Utah, an MRI the next day revealing nothing more than a muscle strain. He has since gotten a second opinion confirming there is no ligament damage, according to the source.
The source said Garnett has no structural damage, only the effects of wear and tear, though he could have a minor arthroscopic procedure after the season.
"We're just going to shut him down until we feel that he's ready," said Rivers. "It's nothing structural, it's the same thing that it's been, it's just not reacting the way we thought it would react.
"Just his gait, he just doesn't look right, and I'm not going to chance that."
The Celtics are being conservative in bringing back Garnett to have him fresh for the playoffs and protect their investment. Garnett has three years remaining on a $20 million annual contract.
Garnett was expected to gradually regain fitness and strength but apparently suffered a setback after playing a total of 67 minutes in four games. He struggled during the Celtics' visit to Orlando last Wednesday (an 84-82 loss), then met with Ainge and Rivers before the visit to Atlanta Friday.
He will miss his third game in succession when the Celtics host Charlotte tonight.
"He's not very happy about it," Rivers said. "He's frustrated, but understanding, I will say that. But he didn't fight it, which tells you as much as you need to know."
Though Rivers hopes Garnett will return April 12 and will be ready for the playoffs, which begin April 20, even those target dates are in question. The fact that Garnett has acceded to the advice of Rivers, team physician Brian McKeown, and trainer Ed Lacerte indicates the severity of the problem.
The plan was to have Garnett take advantage of practice time during the Celtics' five-game homestand, which started with a 103-84 win over Oklahoma City Sunday, but that was scrapped after yesterday.
"The whole key for us right now is making sure he's healthy, regardless if it's three games or even the rest of the season," said Paul Pierce. "The most important thing is his health and, hopefully, getting him back on the court for the playoffs. Only Kevin knows his body; doctors aren't always right.
