With Jaylen Brown missing the All-Star game, the Celtics should now be able to add more players to their roster without risk of running into the luxury tax. Brown still has a number of other bonuses, and Derrick White has some himself, but the C's should be able to make conservative assumptions about these bonuses and still have room. These bonuses include:
Jaylen Brown:
$482,143 -- 65+ games played. Jaylen would need to play 19 of the final 22 games to meet this bonus. Not a given, but presumably yes.
$964,286 -- 65+ games AND 49+wins AND 2nd round of playoffs. The Celtics would need to go 15-7 in the final 22 to reach the wins requirement. Not a given, but within the team's abilities. Obviously there's no way for the Celtics to know about the 2nd round of the playoffs while they can still add players, so they'll assume the latter as a yes. One thing that isn't clear -- I believe the bonus is $482,143 for the wins requirement and another $482,143 for the playoff requirement, so they could be earned separately, but it might be that they're lumped together as one. Public reporting has been questionable on this point.
$1,446,428 -- 65+ games played AND All Star, All-NBA, MVP, DPOY -- Jaylen missed the All-Star game, and the other three ways to earn this bonus don't seem to be in the cards this season.
Derrick White:
$500,000 -- 70+ games played. White would need to play in 17 of the final 22 games to earn this bonus. The Celtics are likely calculating him as making this mark, even though it is currently classified as unlikely for cap purposes.
$250,000 -- All-Defense. White is a very good defender, although All-NBA tends to be a crapshoot. I imagine the C's will plan on White meeting this incentive so as to not hit the tax.
$500,000 -- 185+ 3-pointers. White has made 87 3s on the year, averaging 1.6 made per game. He would need to hit 98 more threes in the final 22 games, roughly 4.5 3's per game. He'd have to nearly triple 3-point rate over the final quarter of the season to meet this incentive. While technically not impossible, I would be surprised if the Celtics have this bonus budgeted in for tax purposes.
Accounting for the $1,446,429 in bonuses Jaylen still has a reasonable chance of earning, as well as the $750,000 in bonuses White can still earn, the C's are left with $1,449,142 in tax space for the rest of the season. This is a little less than the amount needed to sign three players to rest-of-year contracts immediately, but they shouldn't have trouble avoiding the tax if they sign someone to one immediately out of break (they need to have at least added a 10-day by Thursday to meet minimum roster size). By the time other players have cleared buyouts, the C's should be able to add another player immediately, and a third within a few days. That said, my prediction is that they will sign someone they like to a 10-day contract coming out of the break, keeping the other two options open for buyout. If they're able to get 2 buyouts, the 10-day player won't be immediately renewed, and the team will go with 14 for March, filling the final spot in the final days of the season depending on team needs heading into the playoffs. If they are only able to get one player they like off of buyouts, the 10-day player will be renewed and probably ultimately signed to a rest of season deal, maybe with some sort of option for next season. If they strike out on buyouts, look for the person they add next week to be converted to a rest of season deal, as well as two other G-leagues in March/early April.