The Boston Celtics notably refrained from making an offer to star point guard Kyrie Irving last summer, plenty aware that he would decline it once it was extended. According to ESPN's Zach Lowe, the Celtics wanted to make Irving a substantial offer to stay, but were capped at what they could offer by salary cap rules:

The league could broaden access to contract extensions. Boston would have offered Irving an extension last fall, sources say, but rules capped Irving's first-year salary in such a deal at 120% of his 2018-19 salary — well short of what he stood to make by entering unrestricted free agency.

Talks of a looming extension quickly came up in early offseason interviews with Irving, who was coming off an injury-riddled postseason, but he quickly made it known he had no intention to sign a deal in which he could make significantly less than by becoming a free agent the following year.

Due to these constraints, Boston refrained from doling out an offer it knew he would turn down, saving itself a formality but knowing it could be a close call in free agency.

The Celtics ultimately lost out on Irving in free agency, but they were able to salvage the next-best consolation prize in Kemba Walker, who hopes to start clean after a mostly fruitless eight years with the Charlotte Hornets.

League rules might be changed in order to make extensions more feasible, as very few would-be free agents are enticed to take less money and rather wait to become free agents to have a wide spectrum of opportunities.