Kemba Walker is confident in the "high-character, high-energy guys" currently on Team USA despite the amount of dropouts. (1:02)

LAS VEGAS -- When Jaylen Brown got to town last weekend, he was looking forward to trying Mizumi, a high-end Japanese restaurant at the Wynn Hotel.

So on Sunday night, with three of his Boston Celtics teammates also preparing for Team USA training camp, he was pleased they decided to go together. But when Brown, Kemba Walker, Jayson Tatum and Marcus Smart arrived, they were told they couldn't be seated because they were wearing shorts and flip-flops and there was a strict dress code.

"We were in Vegas; we thought we'd be fine," Brown said with a smile.

The group instead went to an Italian restaurant and had their first chemistry-building meal. And it was Tatum, by the way, who picked up the bill, despite it being Walker who just signed a $140 million deal.

"He'll get the next one, as long as it's not me," Brown joked. "That was the first time as a group we got a chance to sit down together. It was the first of many."

The shifting Team USA roster over the past several weeks enabled Brown and Smart to earn invites. Tatum was already on the roster, and Walker had committed before he signed with the Celtics in free agency. It all created an unexpected chance for the established Celtics to get time together with their new teammate.

After so many stars withdrew, Marcus Smart (40) and Jaylen Brown (33) were invited to join Celtics teammates Jayson Tatum (34) and Kemba Walker (26) on the Team USA roster. Ethan Miller/Getty Images

Celtics coach Brad Stevens was scheduled to arrive late Tuesday, and he will get some time with his players, as well.

"I'm the new guy; they already know each other," Walker said. "They are just kind of reeling me in and getting me acclimated to how things go. With four of us here now, it gives us an opportunity to play with each other and learn each other's tendencies."

Left unsaid by the players in Vegas is that chemistry was an issue for the Celtics at times last season. Though this isn't a secret.

Walker's predecessor, Kyrie Irving, had issues with younger teammates and wasn't afraid to say so. Irving also wasn't afraid to say it with his play. Eventually, it became clear he was shopping for a new future as his relationship with now Brooklyn Nets teammate Kevin Durant intensified.

There also was some chafing in the locker room by the slack Stevens afforded Gordon Hayward as he struggled in return from an injury, among other intra-team challenges.

Walker is known for being both hardworking and low-key, but that doesn't mean there won't be an adjustment period. It's too early to say whether this time with Team USA will end up being positive, negative or neutral.

"It can only be positive for us because it's chemistry added," Brown said. "I just want to hoop. I don't want any politics. We're artists and this season is a new canvas."

There is, however, an unusual scenario in which the group is caught up. There aren't a lot of certainties with the Team USA roster. There will be some real competition for the 12 roster spots available for the FIBA World Cup -- which tips off Aug. 31 in China -- and the Celtics might find themselves competing against one another.

Walker is the lone All-NBA player on the roster and one of only three All-Stars, along with Khris Middleton and Kyle Lowry, making him a lock.

Tatum has a strong chance, as he was one of the handful of players on the original roster who kept his commitment to play this summer. But the young Celtics trio might force coach Gregg Popovich to make some difficult decisions.

In the first session of the week, Walker found himself trying to make a tying basket at the buzzer only to have Brown draped all over him to force a miss. In some ways, it isn't unlike an average NBA training camp practice with teammates wanting to beat one another.

But this isn't a team with guaranteed contracts. Some of these guys will be going home, and that's not a position they are used to.

"I'm not sure I think of it as competing for playing time and spots with them," Tatum said. "We're all grateful to be here. Hopefully, all four of us make it; that would be amazing. Me and [Brown] play one-on-one all the time, and we've always tried to push each other and it's been that way since day one. Ultimately, we have the same goal with our teams and here."

Popovich indicated Tuesday he was considering some players from the Select Team, who are in camp to help the senior team prepare and who vastly outplayed the veterans in a scrimmage. De'Aaron Fox and Joe Harris already have been promoted to play with the main squad, and Fox is looking like a legitimate contender to make the team. Trae Young, also on the Select Team, played well in the portion of practice that was open to media Tuesday.

The coach declined to say how he wanted to structure his team, whether he preferred an extra true center or wanted more versatile big men. With so many on the roster who play some version of the wing/stretch power forward position -- including Tatum, Brown, Smart, Middleton, Harris, Donovan Mitchell, Harrison Barnes, P.J. Tucker and Kyle Kuzma -- there might be three or four cuts in that group alone.

There's a chance this won't be a fairy tale for the Celtics -- that is, getting to send their new core to play overseas together and shorten the adjustment period for Walker's arrival. Then again, it could happen. And with the defensive versatility of Tatum, Brown and Smart, it's even possible they could play together for some stretches.

Either way, the four Celtics know this week presents an opportunity, and they're sharing that mindset.

"I just want to jell with those guys as best as I can, kind of get things going as fast as we can," Walker said. "Me being with those guys, it's pretty cool."