Sources: Possible Achilles injury for Bucks' Lillard

Milwaukee Bucks star Damian Lillard will undergo an MRI on Monday to determine the severity of the left lower leg injury that forced him to exit Sunday night's 129-103 Game 4 loss to the Indiana Pacers in the first quarter.

The preliminary examination indicated a possible Achilles tendon injury, sources told ESPN.

"Just being honest, it's not very promising," Bucks coach Doc Rivers said postgame.

Lillard was injured while trying to help secure an offensive rebound midway through the first quarter. After tapping the ball away from a Pacers player, Lillard fell to the ground and grabbed his left leg, remaining down for the next defensive possession.

He was helped to his feet during the next dead ball and needed assistance leaving the court while putting no weight on his left leg. He was escorted to the locker room, and the team ruled him out for the rest of the game.

"I knew it right away," Rivers said. "I felt bad for him; the guy tried to come back for his team. I just felt bad for him."

Lillard was in a walking boot and on crutches when he left the arena.

"When you see a guy like that not able to walk on his own, you know this might be serious," Bucks star Giannis Antetokounmpo said. "Then you hope for best case scenario."

Lillard left the game with 5:57 remaining in the first quarter. The Bucks trailed by only three points (15-12) at the time, but Rivers acknowledged that seeing Lillard go down was deflating for the rest of the team.

"Dame's one of them special ones," Bucks guard Kevin Porter Jr. said. "He's very much needed, very much impactful in every way. Seeing him go down and not be able to return, it's definitely defeating."

Milwaukee trails 3-1 in the series against Indiana. Game 5 is Tuesday in Indianapolis.

Lillard had missed the team's final 14 regular-season games because of deep vein thrombosis in his right leg. He returned in Game 2 of the first-round series against the Pacers after a month out of action in a recovery the team called unprecedented.

However, Lillard had not matched his usual production during this series, averaging 10.5 points and 6.0 assists on 24% shooting (6-of-25) in his first two games. He missed his only two shots in Game 4 before exiting.

"When a guy just works as hard as he can to get back on the court, then those things like that happen, very sad for him," Bucks forward Bobby Portis said. "Sad for us for real. We need him out there."

After Lillard's injury, the Pacers went on a 10-3 run to take a double-digit lead. Indiana was ahead by double digits at halftime for the second straight game and extended the lead for a 26-point victory, the second-largest home playoff loss in Bucks history, per ESPN Research.

"This time of the year, I think everybody gets so caught up in all the antics and the playoff rivalry and all that type of stuff. At the end of the day, this league's a brotherhood, man," Pacers center Myles Turner said. "There's only 450 of us and he's always been one of my favorite competitors since I've been this league. Just thoughts and prayers. You never want to see anything like [that] happen no matter how competitive these playoffs are."

Milwaukee has now fallen behind 3-1 in a playoff series for the third consecutive season. But while the Bucks will await the results of Monday's MRI, they were preparing to be without Lillard going forward as they attempt to avoid a third consecutive first-round playoff exit.

"I think everybody in the locker room knows what the deal is," Antetokounmpo said. "The next guy got to step up. We got to do what we got to do, move the ball, play together, try to win the game and come back."