That didn't take long. After only two days of practices, the Rockets are already banged up down low, though at least Dwight Howard is healthy so far. 

After two days and three practices, the Rockets are beginning to run out of centers. Dwight Howard remains the center of attention, but his predecessor as the Rockets’ starter, Omer Asik, left the floor late in Sunday’s practice with a strained calf muscle. He is listed as day-to-day.

Greg Smith (strained right hip) is also day-to-day and Marcus Camby (plantar fasciitis) is out this week, leaving Howard and rookie Jordan Henriquez available at the position. Guard/forward Francisco Garcia sat out Sunday to rest the sore groin muscle he tweaked at the Tournament of the Americas, but had been practicing.

via Ultimate Rockets » Omer Asik suffers strained calf muscle at Rockets’ camp.

Nothing major, but it's an issue for a team lacking in great depth. That plantar fasciitis for Camby is particularly troubling. That doesn't go away easy, and the Rockets wanted to play Asik and Howard together some, which would mean they need more centers to spell the duo. 

Smith's hip injury is also painful, and hip injuries are slow to recover from. Luckily for the Rockets, they've always been good at finding young players from their D-League affiliate the Rio Grande Valley Vipers, and there's nothing major to keep them out for the start of the season, either.