Breaking news: John Cena has injured his right achilles in a match with Ryback on the European tour.
http://www.wwe.com/shows/raw/2013-04-29/john-cena-injured-on-wwe-european-tour-26111113
Details still sketchy. When Edge tore his achilles in July 2009, he had surgery and was out of action for over 6 months.
You never know with WWE, may just be an angle to make Cena look even better than he is, by beating The Ryback 2/3 weeks after a big injury.