Some rival executives believe the Celtics could have a tough time finding substantial upgrades on the trade market. Their salary-cap situation just isn’t conducive to a big deal. After their top five players (Kemba Walker, Jayson Tatum, Jaylen Brown, Gordon Hayward and Marcus Smart), the team’s next-biggest contract belongs to Daniel Theis at $5 million. That means the Celtics haven’t wasted money in the wrong places, but it also means they don’t have any bloated bench salaries to swing for a high-priced acquisition. Barring an unexpected decision to break up their core, they are limited in whom they can target.