Losing Robert Williams for 8-12 weeks was never going to be easy for the Boston Celtics, especially after they traded Daniel Theis in the Malcolm Brogdon trade. Add in the fact that Al Horford is 36 years old and likely going to need ample rest ahead of the postseason, and Boston was destined to be in a tough spot in the front court.
By the time they learned about Williams’ injury, free agency was all but over. They had already used their MLE on Danilo Gallinari (who unfortunately also got injured), and there was no money left to sign a high-level backup.