The most noteworthy absence involves Matthew Stafford. It's no surprise whatsoever that he didn't practice, as he isn't expected to play this week. Even so, it's interesting to note that Stafford was not wearing a sling at practice, although he was apparently walking in an "awkward" way, likely not wanting to adjust his right arm too much.
The other three starters that were out are all on the defensive side of the ball. Cliff Avril, who actually had surgery on his broken pinky finger yesterday and is also recovering from a knee injury, was out. DeAndre Levy, who hasn't practiced in a while because of a groin injury, was also out. Finally, Louis Delmas was out because of his groin injury, although it's certainly possible that he was just resting rather than couldn't practice.
We won't know for sure who will and won't be able to play until later in the week, but one thing I do know is that I'd be shocked if Stafford played. The minimum amount of time missed seems to be two weeks, and even that appears to be optimistic, so I don't expect him to play on Sunday. As for the defensive players, it's anyone's guess right now.
UPDATE: Shaun Hill has been named the Lions' starting quarterback for Sunday.