Critics have jumped on controversial NBA player Ben Simmons, after the Australian was a late withdrawal from a long-awaited debut for his team the Brooklyn Nets.

With their season on the line, down 3-0 in a seven-game series against Boston Celtics, the Nets needed every player at their disposal for the potential elimination game.

Simmons was widely expected to make his season and team debut in Game 4 after a lengthy ramp-up period while dealing with a back injury.

But ESPN reported that Simmons awoke with back soreness on Sunday, and he and the Nets agreed to play it safe and keep him out.

The former Philadelphia 76ers star was cleared for contact last week and participated in more live drills at practice, including a 4-on-4 drill.

The news of his absence from the key game prompted a storm of criticism from former players and pundits alike.

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Former Indiana Pacers star Reggie Miller, now a television NBA pundit, took to social media to register his frustration with Simmons.

"Cmon MAN!!! Out for Game 4 when it was rumored you were going to make your debut," he tweeted.

"This dude has ZERO competitive (fire emoji).

"As small a chance as the Nets have to come back in this series, you still have KD and Kyrie, all you need is to win ONE game and take it from there. #ManUp."

ESPN presenter Stephen A Smith joined in the criticism on-air.

"This is one of the most pathetic situations I have ever seen in my life," he said.

"He ain't going to war, he ain't going to the octogon (MMA), he's not going in a boxing ring.

The number two seed Celtics defeated the number seven seed Nets 109-103 in Game 3 on Saturday night to move ahead by a daunting margin.

No team in NBA history has ever come back from a 3-0 deficit to win a playoff series.

Simmons, acquired in a blockbuster trade in February that sent James Harden to the Sixers, has yet to play a game in a Nets uniform.

Simmons forced his way out of Philadelphia over a fractured relationship with 76ers coach Doc Rivers and teammate Joel Embiid.

Ahead of his move, Simmons requested a trade in the offseason, refused to attend preseason training, then turned up briefly at a couple of session before paying millions of dollars in fines for not suiting up for the Nets for a string of games.

Philadelphia fans responded to the standoff by chanting for Simmons to be traded during games.

The 25-year-old was the number one overall pick in the 2016 draft. He averaged 15.9 points, 8.1 rebounds, 7.7 assists and 1.7 steals per game with the 76ers.

Reuters / ABC