Within hours of his planned season debut, Brooklyn Nets guard Ben Simmons reported a return of back soreness on Sunday, sources told ESPN, and has been ruled out for Monday's Game 4 against the Boston Celtics.

After approximately 10 days of pain-free ramp up following recovery from a herniated disc, Simmons' admission at the team practice facility was met with surprise and disappointment. On the brink of a sweep to the Celtics, the Nets had hoped Simmons would be in uniform and active with the hope of coach Steve Nash using him in limited minutes, sources said.

While Nash and Nets players had publicly said that they were unsure whether Simmons would finally play in Game 4 on Monday, Simmons and the organization had discussed at length a plan for his debut to come on Monday in Game 4 at the Barclays Center, sources said.

While Simmons hadn't been able to scrimmage with the Nets starters, there was still some hope his presence on the court could provide some help to a flailing team -- and allow Simmons to cross the mental threshold of getting back into an NBA game for the first time since a meltdown against the Atlanta Hawks in the 2021 Eastern Conference Finals as a member of the Philadelphia 76ers set into motion a turbulent 10 months of trade requests, mental health issues and back trouble.

Simmons, 25, is a three-time All-Star and will have three years and $114 million left on his contract beginning with next season.