WALTHAM, Mass. — With 16 players under guaranteed contracts and only 15 roster spots, Boston Celtics General Manager Danny Ainge knows he has some decisions to make.

“All 16 guys are capable of being in NBA uniforms,” Ainge said Friday as the team held its media day. “We have a lot of quality players. We’re going to have a lot of competition and I’m excited about that.”

The Celtics opened training camp this weekend, getting a head start on the majority of NBA teams to make up for a trip to Madrid and Milan. Ainge said there will be a lot of competition for playing time, and it will be up to Coach Brad Stevens to decide how players are used.

“We have a coach who wants to win,” Ainge said. “He gets to decide who gets what.”

One of the biggest questions for Stevens will be whether to start Isaiah Thomas. Thomas averaged 19 points per game – highest on the Celtics last year – and he did it despite coming off the bench and playing under 26 minutes.

The 26-year-old point guard had expressed a desire to start, but Ainge said that was to be expected.

The Celtics reached the playoffs last year as the No. 7 seed in the East after trading point guard Rajon Rondo.

Also Friday, the Celtics announced they signed guards Levi Randolph and Corey Walden and forwards Coty Clarke and Malcolm Miller.