An upbeat atmosphere prevailed Thursday at City National Arena as the Vegas Golden Knights, a team with much to prove, opened their training camp in preparation for their sixth season.

Usually, the focus is on who’s not there. But in the case, everyone’s eyes were on Jack Eichel, who the Knights traded for last season, and captain Mark Stone, who was back on the ice after having back surgery late last year.

It was a time to assess and dissect the lines, the defensive pairs, the goaltending and how quickly this group would pick up new coach Bruce Cassidy’s system.

Cassidy, who spent six years in Boston with the Bruins, didn’t try to force-feed things on Day One. He kept the drills simple for the three groups that participated. A lot of defensive work and getting the players accustomed to competing and winning 1-on-1 battles.

“It was a good day, a work day,” Cassidy said. “We’ve got to get a little more comfortable with people around us because we play a game Sunday.”

The Knights will be in Denver to play the Stanley Cup champion Colorado Avalanche. And Stone, who wore a red non-contact jersey Thursday, will likely be held out of the preseason contest. But he said he’d like to get in a couple of games to get his timing down and find a comfort level with whoever he is ultimately skating with.

“It was good to get back in a structured group,” Stone said.”But I feel good. A little stiff, but it’s a good stiff. I haven’t used some of these muscles in four years.”

Stone skated with Chandler Stephenson and Jonathan Marchessault. Stephenson, who has been a linemate of Stone’s for a while now, said he was impressed with the captain.

“He was moving pretty well,” Stephenson said. “I’m excited to see what he does now that he’s got the surgery behind him and he’s feeling good again.”

Eichel, who is looking at 2022-23 as a fresh start after having responded from replacement disk surgery and then playing the last few weeks of the 2021-22 campaign with a fractured thumb, was paired with Phil Kessel, who was recently obtained from the Arizona Coyotes, and veteran Reilly Smith, who signed a three-year, $15 million contract extension to remain a Golden Knight. The trio looked comfortable working together and while Eichel cautioned it was just the first day, he said Kessel and Smith are talented players.

“We’ll see how it goes, but it was good (today),” Eichel said of having Kessel and Smith on his flanks. “They’re veteran guys and they know how to play.”

Cassidy had hinted he might breakup the team’s Misfit Line of Smith, Marchessault and William Karlsson and he was true to his word, if only for one day. The trio, which had played together since Year One, were assigned to different groups with Karlsson centering for Brett Howden and Michael Amadio in what would essentially be a third line. Cassidy said he will be shuffling things around during the preseason so there’s always the possibility the Misfits get reunited at some point.

But the news wasn’t all positive. General manager Kelly McCrimmon said center Nolan Patrick, who has batted injuries going back to his junior days with the Brandon Wheat Kings and had missed significant time with Vegas last season, will not play this season, joining goaltender Robin Lehner, who has surgery on his hip and shoulder, and Shea Weber, who was acquired from Montreal and is expected to retire when his contract expires. All three are on long term injured reserve.

When McCrimmon was asked if the 24-year-old Patrick, who was the No. 2 overall pick in the 2017 NHL Draft by Philadelphia, may be forced to retire, he wasn’t ready to accept that outcome just yet.

“We’ve talked several times and there hasn’t been progress,” McCrimmon said of the health of Patrick, who was hit in the head by Colorado’s Nathan MacKinnon on Feb. 16 and hasn’t played since. “This isn’t about hockey. This is about real life. There’s no need to make a decision now. But he’s out for the season and let’s see what happens.”

The Knights remain engaged with restricted free agent defenseman Nic Hague, who has not signed and was not at training camp. The Knights, who are up against the salary cap, may not be able to give the 6-foot-6-inch Hague, a former second-round pick who made $863,333 last year, the raise he deserves.

But with no resolution on the immediate horizon, it leaves the door open for someone to make the opening night roster. Cassidy liked what he saw of Kaedan Korczak in the recent rookie tournament in San Jose and veteran Ben Hutton skated with Zach Whitecloud Thursday.

As for the team’s goaltending situation, Logan Thompson looked the best of the six who participated in the first day of practice. He is the likely favorite to be the opening night starter as Laurent Brossoit is still recovering from off-season hip surgery and won’t be participating in training camp. Adin Hill, who was recently acquired from San Jose, and nine-year veteran Michael Hutchinson are Thompson’s competition.

Cassidy said he plans to play Thompson and Hill a lot in the seven-game preseason.

“We’ll let them compete and see where it goes,” he said.

In fact, competition is the watchword for this entire training camp. Even if you’re a cinch to make the opening night roster, where you play and with who will be determined by what your production is. Cassidy will mix and match his lines and defensive pairs, see who is picking up his system the quickest and who is producing.

“That’s what preseason is for,” he said. “We’ve got seven games to sort things out.”

The process is underway.

GOLDEN KNIGHTS TRAINING CAMP LINES/DEFENSIVE PAIRS:

Forwards –

Reilly Smith-Jack Eichel-Phil Kessel

Jonathan Marchessault-Chandler Stephenson-Mark Stone

Brett Howden-William Karlsson-Michael Amadio

William Carrier-Nic Roy-Keegan Kolesar

Defensemen –

Alex Pietrangelo-Alec Martinez

Shea Theodore-Brayden McNabb

Zach Whitecloud-Ben Hutton