It appears Boston can now sign Hayward to the full 30% max, as well as sign Yabusele, and keep Rozier.
The Celtics have the following salaries currently on the books:
Al Horford -- 27,734,405
Jae Crowder -- 6,796,117
Isaiah Thomas -- 6,261,395
Marcus Morris -- 5,000,000
Jaylen Brown -- 4,956,480
Marcus Smart -- 4,538,020
Terry Rozier -- 1,988,520
Ante Zizic -- 1,645,200
Jordan Mickey -- 1,471,382
Demetrius Jackson -- 1,384,750
Jayson Tatum -- 5,645,400
Total -- 67,421,669
By waiving Mickey and adding in two empty roster charges ($815,615 ea.), the Celtics would be at $67,581,517 in salary, leaving them with $31,511,483 in cap space. A max contract for Hayward is $29,727,900 meaning after he is signed Boston would still have $2,599,198 in cap space remaining, enough to sign Yabusele to his rookie scale contract.