Earlier this week, Lin had held out hope of returning in time for Game 4, scheduled for Sunday afternoon. But Lin's surgically repaired left knee hasn't healed quickly enough for him to return to the court yet.
"I haven't been able to load it or jump or explode or drive by somebody the way I want to, so it's going to be longer than that," the second-year guard said.
Lin experienced soreness in his left knee Thursday, a day after scrimmaging for the first time since his April 2 surgery to repair a small meniscus tear in the knee.
"It wasn't the worst, it wasn't the best," he said of the feeling in his knee, adding, "I don't have my full explosiveness."
Lin left open the possibility that he could return for Game 5 Wednesday.
"I really don't want to say I am or am not (returning). I just want to take it day by day. Game 4 doesn't look great. Game 5, I have no idea," he said.
The Heat lead the best-of-seven series 2-0 entering Thursday's Game 3.
Some of his veteran teammates have talked to Lin about the importance of being cautious in his attempt to come back. Lin doesn't want to risk re-injuring himself and has admitted that he may not be very effective when he returns, given the fact that he hasn't played since March 24.
"My mind obviously wants to help but how much can my body help (I don't know)," Lin said. "Having said that, I'm still getting better every day."
Lin is planning on scrimmaging again either Friday or Saturday.
Knicks interim coach Mike Woodson stressed on Thursday he didn't want to rush Lin back to the floor.
"I'm not pushing anything. I'm pushing the guys that are in uniform," Woodson said. "That's what's important to me. It was nice seeing him run up and down yesterday but it's a little different when you're talking about playing playoff basketball and you've got to push and hold and cut and defend guys that are coming at you full speed. We've just go to wait it out and see where we are with him."
Baron Davis has started in place of Lin at point guard for the Knicks. The 33-year-old has dealt with back soreness during the series but said he is healthy enough to play in Game 3.
Ian Begley is a regular contributor to ESPNNewYork.com. Information from The Associated Press was used in this report.