The Beas did not make the flight to Milwaukee with the team because of an illness that was making him feel pretty ishy. Due to the Grizzlies confinement on an airplane for several hours over the next two days, the team chose to have Beasley sit these out.
Personally, as a fan of the hope that MB brings to the back end of the Grizzlies roster, I really hope this doesn't do too much to damage his chances at sticking around. We saw how internal health can derail a player's season last season with Tayshaun Prince (that's my new optimistic view I've adopted to get ready for the season -- "it was the illness, not anything else.")
This is likely to give Earl Clark a few more chances to shine, so Michael Beasley will likely need to recover soon and make a splash to stay in the Grizzlies plans.