As it turns out, it looks like Ugoh missed practice because he is considering giving up football. Tom Kowalski reports that Ugoh is currently pondering retirement, perhaps because he likely will not end up making the team even if he continues playing. Although injuries have left the Lions' depth at offensive tackle very thin, the four spots at tackle are likely to go to Jeff Backus, Gosder Cherilus, Jason Fox and Corey Hilliard.
If Ugoh does in fact retire, ESPN's John Clayton thinks the Lions will sign former Bengals offensive tackle Kirk Chambers.
Look for the Lions to land T Kirk Chambers of the Bengals in the next few days. They have three injured OTs
At this point the Lions just need depth at tackle until Backus and Fox return. Ugoh has helped with that depth, but if he doesn't want to play football anymore there's really no point in keeping him around, so signing Chambers would make sense.