According to Sixers beat writer Kate Fagan, last year's starting center, Spencer Hawes, had tentatively agreed to sign the $4.1 million qualifying offer. By signing the qualifying offer Hawes remains a Sixer for the rest of this season, but becomes an unrestriced free agent at the end of the upcoming season. Hawes was a restriced free agent this off-season, meaning teams other teams could sign him to a contract, in which the Sixers could match. That didn't happen, and the Sixers didn't offer to extend him like they did Thaddues Young, so Hawes will return for one more year, with the rest of his future with the Sixers uncertain.
Hawes started 81 of 82 games for the Sixers last season, and the 23 year-old arguably enjoyed the best season of his career – still nothing to write home about. His offensive numbers were still below average by league standards, and he's had better offensive seasons with his former team – the Kings – but Hawes rebounded and defended better than he has his entire career during his first year in Doug Collins system.
Still, Hawes is one of the worst starting centers in the NBA. I think it's safe to say that after the upcoming season the Sixers will have a new starting center, – whether it's rookie Nikola Vucevic or someone else.