Billups strained his left knee in the fourth quarter of New York's 87-85 loss on Sunday.
"I don't know. I don't know. It's really sore today," Billups said on Monday. "We'll see what happens. We'll see how it goes."
On Monday, D'Antoni described Billups as "very questionable" for Game 2 and probable for Friday's Game 3 -- the first home playoff game for New York in seven years.
"We're just going to treat it and see if I can get better," Billups said. "I think everything is up in the air and day to day. This is the worst time to get hurt in the first round in the first game of a tough series. I know the team needs me. It's just frustrating. But it's kind of the way the ball bounces sometimes and hopefully I can get back soon."
This is now Billups' third injury since being traded to the Knicks along with Carmelo Anthony on Feb. 21. On March 1 against the Magic, he suffered a deep left thigh bruise and had to miss six games. Then on April 6 against the Sixers, he left the game with a right thigh contusion, but he was able to return two nights later against the Nets.
Anthony said Billups' uncertainty for Game 2 is a big concern for the team.
"You don't want to lose a guy like that in the midst of a battle like the one we're in right now," Anthony said. "I just pray it's nothing serious, and just be confident and pray once again he's able to go tomorrow. It affects us big time. We're losing one of our soldiers, our leader, but at the same time it's go-time, it's playoff time. We have to have guys that step up, everybody gotta step up."
Especially Toney Douglas. If Billups is not ready to go Tuesday, the second-year point guard will get the start and 12-year veteran Anthony Carter will back him up. D'Antoni was very pleased with how Douglas performed in his first-ever playoff game. Even though he scored eight points, he never looked rattled and nailed the potentially game-clinching 3-pointer with 37 seconds left to give the Knicks an 85-82 lead.
"Toney played well last night, hit some big shots," D'Antoni said. "You hate to lose Chauncey, obviously, but at the same time we feel good. Toney's gonna just have to save his energy up. He's gonna play a lot of minutes."
During the regular season, Douglas averaged 10.2 points and 2.7 assists in 23.8 minutes off the bench, but as a starter in nine games (eight due to Billups' DNPs), he improved his numbers to 13.9 points and 5.7 assists. Most impressively, he improved his scoring every month from December to April, finishing the last month of the season averaging 14.4 points. Not to mention, he led the league in most 3-pointers made after the All-Star break (68). He also ended with two stronger months distributing the ball, averaging 4.7 assists, which was a concern of D'Antoni's earlier in the year.
In preparation for the playoffs, Douglas said he's had to adjust to bigger playbooks, as well as longer practices and film sessions, but he has a lot of confidence going into Game 2. If he gets the call Tuesday, he may look to run more offensively to try and tire out an older Celtics team. He plans to talk to Billups more about Game 2 strategy when they arrive back at the hotel Monday afternoon, but he's already learned quite a bit from Mr. Big Shot.
"A lot of things -- just talking to him, just being smarter as a player," Douglas said. "It's not always about outrunning people, out-quickness or being more athletic. I'm just picking his brain and learning a lot of wisdom from him, like with timing and scoring, know when to push the ball and know when not to, know when to give people the ball."
With Billups most likely out (he plans to be in the arena either way), it'll be up to Anthony and Amare Stoudemire, especially, to give Douglas direction on the court.
"As leaders of the team, we have to make sure we keep him motivated," Stoudemire said. "We have to teach him what it takes to win in the playoffs, how to keep his composure and never get out of control. We've got confidence in him."
Jared Zwerling is a senior researcher for ESPN The Magazine and a regular contributor to ESPN RISE. Information from ESPN.com's Chris Sheridan and The Associated Press was used in this report.