Teams have been inquiring about the Celtics’ first-round draft pick that they will receive from the Brooklyn Nets in June—it figures to be a top-five selection—but there is an understanding that it would come at a cost. As of late Thursday night, a league source said, the Celtics had not engaged in any trade talks of real substance. A report on Thursday linked the Celtics to Timberwolves guard Shabazz Muhammad, but one source said that Boston was not interested in acquiring the 23-year-old before the deadline.