CHICAGO -- Joakim Noah missed practice for the third consecutive day on Monday because of personal reasons. His status for Tuesday's preseason opener against the Memphis Grizzlies remains uncertain.

"That will be a game time decision," Bulls coach Tom Thibodeau said after Monday's practice.

Thibodeau hasn't stated publicly what Noah is missing practice for, but Noah acknowledged last week that his grandmother passed away on Oct. 1.

Thibodeau said veteran center Nazr Mohammed will start if Noah can't play.

"I feel good about that," Thibodeau said. "We have a lot of flexibility. Naz will start if Jo doesn't go. Of course Taj (Gibson) could play the five. (Kyrylo) Fesenko, so we feel good about that. But we could also play Vladimir (Radmanovic) more at the four and Taj at five. They're different things we could get to, so we'll be fine."

Thibodeau knows that it will be different with a veteran such as Mohammed in the backup center role that Omer Asik held for the past two seasons. But he's confident Mohammed will be able to hold his own.

"They're different," Thibodeau said. "Different strengths, different weaknesses. Of course Nazr's been 15 years in the league. A lot of big game experience. Skilled offensively, can hit open 15-, 17-footers. A good solid shot blocker. Very good on the offensive boards. And he helps you execute. All he has to do is do his job. We're not asking him to be anything other than who he is."