In fact, they don't want to wait for free agency to begin either.
According to Yahoo/The Vertical's Adrian Wojnarowski, the Celtics are 'pursuing an aggressive summer plan of sequencing the signing of free agent Gordon Hayward and relinquishing the assets needed to complete a trade for Paul George'. They also can entice IN with young players such as two-way forward Jae Crowder, shooting guard Avery Bradley and 2016's No. 3 overall pick, Jaylen Brown. The Celtics hope to receive a commitment from Hayward, who will be a free agent, before then moving the requisite pieces to IN to add George. Boston has contingencies in place to make deals and start a possible Hayward-George scenario toward fruition, league sources told The Vertical. The Celtics have several young players and are flush with draft picks in the coming years. Also according to The Vertical the Celtics and Pacers were close to a deal on draft night but a third team pulled out stalling the talks. He added that Boston is becoming more willing to trade a significant trade package to get a deal for George done.
The Pacers are fielding trade offers for Paul George.
One potential issue could be that the official start of free agency is not until July, and the Pacers may be unwilling to wait until then to move George. But, after telling management that he would be heading elsewhere in 2018, George has been on the trading block ever since.
George is a four-time All-Star and one of the NBA's elite two-way players.