WALTHAM, Mass. — As the Celtics spend the weekend working on the all-out recruitment of free agent Gordon Hayward, and licking their wounds from losing out on a trade for Paul George, rookies and second-year players who could play a significant role on next year’s team are traveling to Utah for the start of summer league.

Fellow No. 3 overall picks Jaylen Brown and Jayson Tatum will play in Salt Lake City and Las Vegas secure in knowing they are featured in the plans. But with much of last year’s frontcourt in doubt, there may also be multiple spots open in the paint surrounding Al Horford.

Jonas Jerebko is an unrestricted free agent, Amir Johnson signed with Philadelphia on Saturday, Kelly Olynyk is a restricted free agent, according to reports Tyler Zeller's contract option wasn't renewed, and Jordan Mickey has yet to find his footing in two NBA seasons. That means players like 2016 first-round pick Ante Zizic and 2017 second-round pick Semi Ojeleye could be in the mix to make an impact right away as rookies.

Zizic, along with Tatum, was officially signed to a contract on Saturday, which means he will be in Boston this season after playing a year overseas in Croatia and Turkey. He averaged 20.0 points and 9.2 rebounds per game in 24 games in the Adriatic League before moving on to play for former Cleveland Cavaliers coach and Framingham native David Blatt in the Turkish League and Euroleague.

“Ante has looked pretty good,” Celtics summer league coach Jerome Allen said. “He competes, and he’s physical, and he’s coachable.”

The 6-foot-11, 254-pound center said he hopes to bring “rebounding and toughness because that’s my style of game” and added “they told me that is my role, so I will do that.”

Allen said he’s already been doing it plenty through three days of summer league workouts.

“Rebounding the ball on the offensive end is almost a complete function of effort,” Allen said. “He never assumes that every shot is going in. But he assumes he has the ability to get every rebound. That’s been a pleasure to see.”

While Zizic could work his way into the rotation through rebounding alone on a team where that was among its biggest weaknesses last season, Ojeleye will have to navigate several routes onto the floor though his myriad skills. With a 6-foot-7, 241-pound body of a power forward, and athleticism of a small forward, to go with a 42.4 percent 3-point shooting percentage in his lone season at SMU, his game is all about versatility.

“Wherever we’ve placed him on the floor, at either end, he’s accepted the task,” Allen said. “[Friday] night, he had a pretty good practice. He was able to get out in transition, was running, and was able to get a few easy baskets.

“I think he has the potential to be a significant player in this league for a long time.”

Ojeleye averaged 19.0 points and 6.9 rebounds at SMU after transferring from Duke and having to sit out a year.

“Going to a place like Duke is a great opportunity,” he said. “I just felt like I needed a fresh start, time to really get myself together as a person, and from there get back out on the court. The biggest thing with me is having a connection with the coach. And I feel I kind of lost that with Coach [Mike Krzyzewski] at that point in my career.

“I think I lost my confidence at some point there and felt like I wasn’t in the plans moving forward. I wanted a bigger role and I felt like I needed to go someplace else to get it.”

Projected as a late first-rounder, he slipped to No. 37 where the Celtics took him in the second round. He said he is looking forward to learning from Celtics veteran Jae Crowder — a player he said he’s been compared to often — as he looks to feed the league’s growing thirst for the so-called “3 & D” player who carves out a role through locking down on the defensive end, while still being able to hit the open jumper from long distance.

“You have to be able to do multiple things on the court,” Ojeleye said. “That’s a label for it. You need to be able to defend. That’s a big part [of the game]. The 3-point shot now is obviously big in the game. It’s a term that’s thrown around a lot.

“But it is a big-time thing. It keeps guys in the league, keeps guys getting paid.”