James underwent surgery to repair the break on Friday but said he's still dealing with pain, soreness and headaches that might force him to miss only his second game of the season.
The team confirmed to ESPN.com that James cleared the league's standard protocol to rule out a concussion.
James sustained the injury when he was inadvertently struck in the face by Serge Ibaka as he drove to the basket midway through the fourth quarter of Thursday's win in Oklahoma City.
The Heat haven't been accustomed to practicing without James, a four-time league MVP who has led Miami to NBA championships each of the last two seasons. But James sat on the side of the practice facility as the team worked Saturday and did some light shooting after the workout.
"It's a little bit of everything -- pain, headaches," James said. "Hopefully it'll get better the next couple of days, hopefully it gets better the next day. But if not, I'm not going to rush it. I feel better today than when it happened. I'm not bleeding. I'm a game-time decision, more probable than anything."
James said he has not yet been fitted for a protective mask, but was expecting to sort through some options later Saturday. He said he still has the mask he wore during his rookie season a decade ago when he fractured his cheekbone while playing with the Cleveland Cavaliers. James said his wife, who was back in their Ohio home, just happened to find the mask on Friday.
The Heat spent Saturday preparing to be without James, whose only other absence this season came when he sat out a Dec. 28 win in Portland because of a strained groin and a sprained ankle. James seemed optimistic about playing Sunday, but he also suggested the final decision would be made by coach Erik Spoelstra and the team's medical staff.
James said he would not be able to play if the Heat had a game Saturday.
"We'll just continue to re-evaluate him," Spoelstra said. "He went to the doctor yesterday to get everything straightened out and corrected. He's feeling better, not good enough to go. But we'll have to see how he feels day by day. We'll see if the swelling (subsides) and how he feels."
The Heat have a number of alternatives if James is unable to play Sunday. Michael Beasley started at small forward when James missed the game in Portland, and veteran Rashard Lewis could also be an option at the position.
The team had a much easier time figuring out jokes to crack on James, who wore a thick bandage on his nose and also spent the past two days poking fun at himself on social media.
"He's Iron Man," Heat center Chris Bosh said. "Sometimes, when you have a broken nose, you have to rest a little bit. So he's just got to rub some dirt on it, do whatever he does and come back healthy. If you come to the gym, you're fair game. We got a couple of big-nose jokes in there. It's good for camaraderie. You can't be sensitive in this locker room."
The injury comes at a time when James is in the midst of perhaps his most productive stretch since he joined the Heat before the 2010-11 season. He had 33 points and seven rebounds in Thursday's 103-81 win against the Thunder despite leaving the game with about six minutes to play.
During the Heat's four-game winning streak, James has shot 61.3 percent from the field and has averaged 37 points, 9.5 rebounds, 5.3 assists and 3.3 steals. James said it would be difficult to adjust to wearing a mask if required. He also didn't believe Ibaka intentionally hit him in the face on the play, but that a foul should have been called.
James said coming back immediately from the broken nose presents a different challenge than when he quickly returned from the fractured cheekbone a decade ago.
"I was a 19-year-old recovering compared with a 29-year-old recovering -- and it's been a long time since I was 19," said James, who could get an entire week of rest if he sits out Sunday and returns Thursday against New York. "I'll get back on the floor. If it's not (Sunday), then I'll get prepared for Thursday."