PORTLAND, Ore. — Rajon Rondo knows the struggle. He endured it his first year with the Celtics.
“I’ve been through 18 of this,” he said recently.
The “this” is losses, and the Celtics lost that many in a row — a franchise record — during his rookie season in 2006-07.
The Celtics’ longest losing streak since that skid now stands at eight after the team lost, 112-104, to the Portland Trail Blazers Saturday night at the Moda Center.
“We’re not getting what we want, and I’m sick about that,’’ coach Brad Stevens said. “But at the end of the day, laying down is not an option. Doing things and continuing to go after it every day is what you do when things get tough.”
Rondo can’t do much to help his team right now, as he’s still sidelined from knee surgery to repair a torn anterior cruciate ligament. He said he’s close and that he expects to return at some point before the mid-February All-Star break.
In the meantime, Rondo can do little more than encourage his teammates.
“Just trying to keep guys confident and positive, just keep being a vocal leader out there, what I can do from the sideline,” he said.
Rondo’s teammates said he has done his best to keep them upbeat.
“He’s one of the most positive guys in the locker room,” said Avery Bradley, who scored a game-high 25 points against Portland.
“It’s hard, not only being a young team, but going through adversity sometimes, guys can go their separate ways, but having veterans like him and Keith [Bogans] and Gerald [Wallace], they’ve been keeping us all together and letting us know that if we just keep working, we can turn this thing around.
“We lost eight in a row, we can turn it around and win eight in a row,” Bradley added. “We just have to stay positive and keep working.”
Does it help them to know that Rondo might be coming back soon?
“We would love to have Rondo back, but the main thing for him is just getting comfortable and heal all the way,” Bradley said.
“That’s all we want for him. We’re his brothers and we want him to come back 100 percent, because we know he’s going to bring a lot to this team.”
Jared Sullinger also said other veterans in the locker room have offered advice.
“They just say, ‘Just keep playing through it, keep pushing through it, you’re going to get out of it sooner than later,’ ” Sullinger said.
Bradley added, “I hope it makes everybody hungry, because this is kind of embarrassing.”
Sullinger has moved to the bench for the last three games, with Kris Humphries replacing him in the starting lineup.
In eight games entering Friday night’s loss at Golden State, Sullinger just wasn’t his old self, averaging just 7.4 points and 6.9 rebounds over 21.6 minutes per game.
Part of his struggles were tied to the lingering pain from a deep bone bruise in his left hand that he suffered Nov. 25 at Charlotte.
Sullinger has had two double-doubles in the last two games, recording 14 points and 10 rebounds against Portland after totaling 21 points and 11 rebounds the night before against the Warriors.
“I could [not] care less who starts or who comes off the bench,” Sullinger said. “I’m just playing basketball and it’s kind of been helping our basketball team, me coming off the bench. As long as we keep fighting the way we did today and yesterday, I’m going to support the move 100 percent.”
As for his hand, Sullinger said, “It’s not going to get no better. It’s not going to get no worse. Just gotta keep grinding through it, just playing through it.”
Going hot, cold
The Celtics have had several scoring droughts at inopportune times during their losing streak.
A key drought Saturday came when the team missed six straight shots during a stretch in the final two minutes when they were trying to come back and steal a win from the Trail Blazers.
The Celtics had similar droughts in close losses to Golden State and the Los Angeles Clippers on this trip.
“We’ve done that — and for whatever reason, we’ve done that in all these games,” Stevens said.
“If you tell us before the trip that you’re going to play and have a chance within two possessions of the Clippers and a possession of the Warriors, and then a couple of possessions here, you’d have felt pretty good about, hey, you’ve got a shot to win at three contenders for the West.
“But at the same time, those droughts are killing us. I think we can get better in those. You know what I’m trying to figure out is, is it because we’re really playing at a high level the rest of the time? That’s the encouraging part.”
Sullinger said he believes their scoring droughts are a product of poor ball movement.
“But when that ball’s hopping from side to side, we’re playing as a team and we’re playing together, it’s a beautiful sight to see,” he said.
Against the Trail Blazers, the Celtics shot 61.9 percent from the floor in the first half, and the ball movement was crisp.
Still, Wallace pointed out that hot shooting is not an indicator of how well a team is playing — or moving the ball.
“When we shoot the ball good, we play pretty good, we keep ourselves in the ballgame,” Wallace said. “It’s the nights when we don’t shoot the ball good is when we get embarrassed.
“And tonight, we shoot almost  percent in the first half and we were only up 2 points. That should tell you a lot right there.”
So, is there an issue on the defensive end?
“I think so,” Wallace said.
“We’ve got to get back to focusing on defense first, getting stops. Right now, our defense depends on how our offense is going. We’ve got to turn that around and make our defense work for us, get stops, and then let our defense make us more offensive-minded.
“We hardly ever get easy baskets or in transition. All our baskets seem like they’re hard. We’ve got to make teams get back in transition like they’re doing on us.”