WALTHAM, Mass. – “We’re in some quicksand right now.”

Rookie Marcus Smart made that comparison after Saturday’s practice in Waltham, Mass. and the Celtics are very much looking for a lifeline to pull themselves out of a 3-0 series deficit. They’re trying to remain focused on the immediate task at hand, which is winning Game 4 against the Cleveland Cavaliers, and not worrying about the bigger picture, which is winning their next four games to advance to the next round.

“We have to be ultra-desperate and ultra-urgent because of where we are, but we pretty much play that way anyway,” Celtics coach Brad Stevens said of being down in a 3-0 hole.

The bottom line is this: you can’t win four games in a row without winning one game in a row.

Brandon Bass, who doesn’t talk much, was clear and concise when describing where the collective head of his teammates was at heading into Sunday’s Game 4.

“Fight to play another day,” Bass said of the team’s mentality. “I think Coach is preparing us to go out there to give maximum effort to compete and go out there and win.”

Along those lines, Stevens didn’t mention it to the media, and no one asked him about it, but he may be making some changes to the starting lineup for Game 4. Avery Bradley indicated as much when he talked to reporters, and when Jae Crowder was asked if he was starting, he confirmed that assertion. It’s unclear if those changes are official or final.

“I think our lineup is different tomorrow and we’re just going to go out there and play as hard as we can,” Bradley said. “I think a few people are starting different. I think, I’m not sure, but I think they might change the lineup tomorrow.”

One player who did not see the floor at all on Saturday is Jared Sullinger, who is nursing a bruised tailbone and is considered “probable” for Game 4. Isaiah Thomas, who played just 21 minutes and scored just five points during Game 3, said he’s ready for Game 4 and that it’s on him to “play well enough so that coach can’t take me out.”

Regardless of who starts, who comes off the bench, and who finishes the game, everybody is aware that they have to be better on the glass to have any shot at winning Game 4. Cleveland’s knack for coming up with offensive rebounds has been leading to second-chance points and back-breaking 3-pointers.

“The thing with rebounding, it’s just a mindset of putting a body on the guy you’re guarding,” Bass said.

The other thing that’s killed the Celtics has been the transition game, specifically when the Cavs have put together multiple buckets in a row.

“I think we have to be opportunistic in transition regardless of scenario,” Stevens said. “What we can’t do is have turnovers late in the half, like we’ve had, multiple times now, and let them go on those 12-0 runs.

“Those runs right now, they have really hurt us. It’s happened in each game at one point or another.”

If it continues to happen in Game 4, that will likely spell the end of the Celtics’ season. The slow climb out of the quicksand starts at 1 p.m. on Sunday.