The Boston Celtics plan to sign free-agent center Aron Baynes to a one-year, $4.3 million contract, according to a league source.

The 6-foot-10 Baynes, born in New Zealand but an Australia national, averaged 4.9 points and 4.4 rebounds over 15.5 minutes per game last season in Detroit. Baynes provides much-needed help on the defensive glass; he grabbed 21.6 percent of all defensive caroms when he was on the floor last season.

The Celtics can't officially sign Baynes until a sequence of moves that will include first signing Gordon Hayward. Boston traded Avery Bradley to Detroit last week to generate the necessary cap space to sign Hayward to a maximum-contract salary that starts at $29.7 million for the 2017-18 season.

The Vertical first reported Baynes' signing.

The Celtics were thin up front with the recent departures of Kelly Olynyk (four years, $50 million with Miami) and Amir Johnson (one year, $11 million with Philadelphia). Baynes adds a bruiser to Boston's big-man depth chart; the only other veteran is Al Horford.

While the Celtics have a bunch of players capable of playing as undersized 4s, the team is thin on pure centers. Boston's frontcourt is likely to be filled out with first-year players Ante Zizic (2016 first-round pick who played last year in Croatia and Turkey), Daniel Theis (undrafted, played last year in Germany) and Guerschon Yabusele (2016 first-round pick who played last year in China and the G-League).

Baynes playfully hinted at his Boston signing on social media Sunday afternoon.

Does anybody know if there's good BBQ in Boston? Asking for a friend 🤔☘️ — Aron Baynes (@aronbaynes) July 9, 2017

The Detroit Pistons owned a net rating of plus-5.2 with Baynes on the court last season, best among the team's regulars. Detroit posted a defensive rating of 105.3 for the season, but that number plummeted to 98.5 with Baynes on the court. Baynes' overall rebound rate of 15.8 was third on the Pistons -- trailing Andre Drummond and little-used Boban Marjanovic -- but that number would have easily led the Celtics. Olynyk topped Boston regulars with a rebound rate of 13.1 last season.

Baynes, 30, is a veteran of five NBA seasons. He began his career with the San Antonio Spurs in January 2013 and has averaged 5.2 points and 4.1 rebounds over 14.1 minutes per game for his career.