"I doubt he'll play tomorrow," said Rivers. "Again, there's a chance, but I doubt it.
"[Garnett] did some running on the treadmill and all the stuff in the weight room. We were on the floor, we went full-court, so he couldn't [participate]. He did do some sliding up and down, I just don't think he's ready yet."
Garnett has sat out the last seven games after suffering a strained right calf in a loss to the Detroit Pistons in late December. The Celtics are 4-3 in that stretch, losing their last two games, which Rivers suggested has Garnett fighting to get back on the court.
But Rivers is trying to prevent him from rushing back too soon.
"He's just not ready yet," said Rivers. "He's close, very close. But you know how I am with that. I think he wants to play, I'll put it that way. I just don't think he should play yet."
Meanwhile, Celtics center Kendrick Perkins hoped to resume full-contact, full-team exercises Tuesday, but said that plan has been delayed a week as team physician Dr. Brian McKeon suggested giving his surgically repaired right knee an extra week to heal.
Perkins still went through skeleton drills and worked out, but full-team contact won't come until next week now.
"[Perkins] didn't do anything live," said Rivers. "We went pretty hard and I didn't want him out there in that. He did skeleton stuff, did some running up and down. But we had a lot of contact and I didn't want him to be part of that."
Perkins tore his ACL in Game 6 of the NBA Finals and underwent surgery a month later. He admitted he's eager to get back on the court, but he also realizes he's just five months removed from surgery and knows another week won't detour him.
In fact, Perkins said he's still targeting a late-January return, suggesting he needs a mere two weeks of practice to shake the rust. Perkins is also getting over a short bout with a stomach bug, which he suggested might simply have been a mild case of food poisoning.
"I'm anxious to get back out there," said Perkins. "At the same time, I know it's in my best interest [to wait]. One more week is one more week."
Celtics guard Delonte West got back on the court Monday for the first time since fracturing his right wrist in mid-November and got up shots for a second straight day Tuesday. He's extremely limited in what he can do, but he expressed great satisfaction in being able to participate in basketball activities.
"I'm not allowed to catch the basketball or dribble it just yet," said West. "I'm getting there. Honestly, just to get some work in, it's a positive."
West hesitated to pinpoint a date for his potential return, but acknowledged that he'd like to be back -- or at least back practicing -- before the All-Star break (Feb. 18-20).
Chris Forsberg covers the Celtics for ESPNBoston.com.