I don't think if this was the problem but if you remember towards the end of the match between Gasquet and Djokovic it looked like Richard landed on his leg, at first glance it didn't look bad but maybe now it's got worse??
I would like to think that he's just being very sensible with his scheduling and making sure he's ok for Wimbledon. Better to miss Queens by far. Also re match practice there are grass courts in Paris.
Richard Gasquet Gilles Simon Rafa Nadal Stan Wawrinka David Nalbandian Andy Murray
Hope he can play Wimbly but with no prep tourney, it'll be difficult to adapt on grass. he's so unlucky especially because Fish, Nole and probably Murray pulled out of Queens, he could have had a real chance to win