Philadelphia 76ers star Ben Simmons will undergo further testing on his injured back Monday after going through initial testing on Sunday, according to Adrian Wojnarowski of ESPN. Simmons will be out for Monday's game against the Atlanta Hawks, and there is a level of concern in the Sixers organization about the seriousness of this injury.

Simmons left Saturday’s contest against the Milwaukee Bucks in the first quarter and did not return. He also previously sat out Thursday's game against the Brooklyn Nets due to lower back tightness.

Nonetheless, the Sixers will certainly need Simmons back into the lineup as soon as possible. The 23-year-old has played phenomenal this season, averaging 16.7 points, 7.8 rebounds, and 8.2 assists in 35.7 minutes per game. Simmons is also shooting 58.5 percent from the field.

Simmons is arguably the Sixers' best perimeter defender this season, averaging a league-best 2.1 steals per game. If Simmons is sidelined, Philly's defense will take a hit. The former Rookie of the Year also leads the NBA in the most pass deflections and the most defensive loose balls recovered.

Until Simmons returns, the Sixers will have to rely on Raul Neto, Alec Burks, Josh Richardson to be their primary ball handlers. Simmons' absence could certainly be an issue for the Sixers, who are seeking to move up in the Eastern Conference standings.

The Sixers are currently the fifth seed in the Eastern Conference with a record of 35-22. On a positive note, the next three games will be against non-playoff teams. Philly can only hope Ben Simmons will not be out long.