Contract talks begin with Tyler Zeller, Jared Sullinger

Tyler Zeller averaged 10.2 points and 5.7 rebounds last season.Barry Chin/Globe Staff

Celtics president of basketball operations Danny Ainge said he has had preliminary contract talks with the agents for forwards Tyler Zeller and Jared Sullinger. Both players are eligible to be offered extensions prior to the Oct. 31 deadline, though it remains unclear whether the Celtics will choose that route for either.

“Obviously, those are two guys that we like moving forward,” Ainge said. “So, yeah, there will be more discussions with both of them, probably during the month of October.”

Forward Perry Jones, who was acquired in a trade with the Thunder in July, is also eligible for an extension. But he is not a lock to make the final roster this fall.

Zeller, 25, appears the most likely of the three to be in line for an extension. The 7-footer averaged 10.2 points and 5.7 rebounds last season and shot a team-high 54.9 percent from the field. Zeller’s win share of 6.5 — a metric that measures the amount of victories contributed by a player — was the highest on the team.

Sullinger, who averaged 13.3 points and 5.1 rebounds in 58 games last year, is still just 23. But he already has had back and foot surgeries, and his conditioning has been a frequent issue. Sullinger has been training in Houston with former NBA player and coach John Lucas for much of the summer and has shared pictures of his apparently trimmed-down physique through social media. But his return to Boston for preseason training will be most telling.

The Celtics currently have 16 players under guaranteed contracts, and they will have to reduce that number to 15 by the start of the regular season. Ainge said no moves were imminent and that he planned to use training camp as an evaluation period to help him decide how to proceed.

Boston has agreed to nonguaranteed deals with guards Coty Clarke (Arkansas), Corey Walden (Eastern Kentucky), and Levi Randolph (Alabama), and forward Malcolm Miller (Holy Cross). All four players will take part in training camp, bringing the preseason roster to its maximum of 20 players.

The Celtics will hold practices in Waltham during the last week of September before leaving for Europe Oct. 2. They will face Olimpia Milano in Milan Oct. 6 and Real Madrid in Madrid Oct. 8.

“I think it can help [team chemistry],” Ainge said of the trip. “I prefer to stay closer to home than go someplace that has a six-hour time change, but they give us a few extra days of camp, which is good.

“Hopefully our guys will get to spend some time with each other in Europe and get to know each other, especially our new guys.”

Re-up with Red Claws

The Celtics and the NBA Development League’s Maine Red Claws have extended their exclusive affiliation through the 2017-18 season. The teams have had a partnership since the Red Claws’ opening season in 2009-10, and in 2012 the Celtics became Maine’s lone affiliate and took over its basketball operations.

Last season, the Celtics assigned a total of six players to the Red Claws, including former first-round picks James Young and Marcus Smart.

“Having [the Celtics’] expertise on the basketball side of things has been huge,” said Red Claws chairman Bill Ryan. “And from our perspective, it’s a huge plus, because our fans can see guys that are going to go on and become contributors for the Celtics, or maybe already are contributors.”

Red Claws coach Scott Morrison was tapped by the Celtics, and he implemented a system similar to the one run by Boston coach Brad Stevens. Last season Morrison was named the D-League’s Coach of the Year.

“The Celtics know that if they send James Young or someone like that to us, he’s going to be in a system he’s comfortable with,” Ryan said. “The calls are the same, the movements he’s supposed to make are the same.”

The Celtics will have three rookies — Terry Rozier, R.J. Hunter, and Jordan Mickey — this season, so there is a good chance the shuttle to Portland will be active once again. Also, up to four players released following training camp can be allocated to Maine.