PHILADELPHIA -- As the Philadelphia 76ers and Ben Simmons' management team work with doctors to evaluate a course of action on the All-Star guard's injured back, Simmons is expected to be sidelined for an undetermined period of time, league sources told ESPN's Adrian Wojnarowski.

The anticipated length of time missed and next steps in remedying his back injury could be decided as soon as Tuesday.

The injury will have longer-term implications than simply the 76ers' upcoming West Coast road trip.

"I don't know," Sixers coach Brett Brown said before Monday night's game against the Atlanta Hawks when asked how long Simmons will be sidelined. "It really is kind of, like, how long is a piece of string? Who knows? Who knows?

"Whatever the time equals on days, games, period of time, then we can talk more honestly as this thing shakes out, but as it sits right now, that's how I see the world."

Simmons, who played less than five minutes in Philadelphia's loss to the Bucks on Saturday night before exiting with back soreness, was described by sources as emotional after leaving the X-ray room at Milwaukee's Fiserv Forum.

He also missed Thursday's overtime win over the Brooklyn Nets with lower back tightness.

Simmons, 23, was ruled out of Monday's game. The team said a further determination on a course of action will be decided within 24 hours.

The team declined to put any sort of time frame on how long Simmons would be sidelined.

What is certain, however, is that the Sixers are going to be without Simmons for the immediate future, which includes a trip to Los Angeles to play both teams there Sunday and Tuesday as part of a weeklong trip through California.

Brown and the Sixers had hoped to spend the opening weeks after the All-Star break solving their yearlong issues on the road (Philadelphia entered Monday with the league's best home record at 26-2, while having one of the worst road marks at 9-20).

Instead, Brown now must figure how he's going to survive without his lead ball handler and one of the two pillars of his team, alongside center Joel Embiid.

"It's not ideal," Brown said. "But that's why you have a team. Now, coach it.

"This is the opportunity we have without an NBA All-Star, without a starting point guard, and we will manufacture ball carriers with the group that's been left back outside of Ben not being with us, and what that role looks like and who has that responsibility."

Brown said the Sixers will not try to replace Simmons, who entered Monday averaging 16.9 points, 7.9 rebounds and 8.3 assists this season, with one player, instead opting for a "point guard by committee" approach. Monday night saw second-year guard Shake Milton start in place of Simmons against the Hawks.

Meanwhile, the Sixers still have to sort out what else is going on with their team.

Al Horford's role continues to be in flux. After coming off the bench the prior three games -- against the LA Clippers before the All-Star break, and then both Thursday against Brooklyn and Saturday against Milwaukee, he was re-inserted into the starting lineup Monday night.

Brown repeated the line he used Friday about Horford's awkward first season with the Sixers after signing as a free agent last summer.

"I have to help him help us," Brown said Monday.

The lack of shooting across the roster remains a problem, as is Philadelphia's ongoing issues away from home. All of that together has left the Sixers, who were expected to be challenging for the top spot in the East with Milwaukee this season, in fifth place in the conference with 25 games to go -- and currently in line to face former Sixer Jimmy Butler and the Miami Heat in the first round of the playoffs.

But as he waits for an update on just how long Simmons will be sidelined, Brown tried to maintain a positive outlook on what the Sixers can learn about themselves with their star guard watching from the sidelines.

"There's 25 games left," Brown said. "It's an eternity. Just keep going back to the end game. What's the bottom line? I'll say it again: If you get the health and the spirit, it's got a chance to equal form.

"It's all about landing the plane. That's what the playoffs are. There's 25 games left. We've taken a hit with Ben. I do see it this way. I'm not spinning it. It's an opportunity for us to learn, and something will emerge.

"We need something to emerge. We're going to learn something, and find something. If this were six games out? I wouldn't be telling you this story. When it's 25 games out, it's with all my heart what I think. That's what I said to my team, that's what I really think and that's what I'm going to try to pull off."