It's a good decision, the bad decision was to play DC and Metz
You know very well that the French media would have killed him, had he withdrawn from DC.
Today the usual French sites, l'Equipe, RMC and WLT also had the news of Richard's withdrawal from Shanghai, but no word about the seriousness of the injiury or his plans for the rest of the year.
I think there are two possibilities. Either the ellbow is worse than he thought before, or he really wants to make an effort at the end of the year, notably in Bercy and saves himself the journey to China to be ready for that.