The Boston Celtics have signed forward Jaylen Brown to a contract extension, beating a Monday deadline to extend the player who has emerged as a key part of the team's future.

The four-year deal could pay Brown as much as $115 million, a person familiar with the negotiations told The Associated Press. The total includes incentives, according to the person, who spoke on the condition of anonymity because terms of the deal were not announced.

"Jaylen has made tremendous strides over the last three years and has become a fantastic player for us on both ends of the court," said Danny Ainge, the team's president of basketball operations.

"He's a great person and hard worker who, at 22 years old, can score and defend against the best players in the NBA," Ainge said. "Jaylen is a true professional who did a great job accepting his role last season, and he is a major part of our championship goals."

The third overall pick in the 2016 draft, Brown averaged 14.5 points and almost five rebounds in his second year, when he was 21 and the Celtics finished second in the East and took the LeBron James-led Cavaliers to seven games in the conference finals.

But last year, Brown averaged 13 points and closer to four rebounds as the Celtics were eliminated in the second round by the Milwaukee Bucks. Since then, Al Horford and Kyrie Irving have opted out of their contracts, and Kemba Walker was signed as Ainge tries to rebuild without further dropoff.