It turns out that John Cena wasn't hurt as much as originally expected. When doctors examined him, they found only a partial tear triceps. This was known when WWE announced Cena's original recovery time.
There was talk of Cena still staying out of action until January but with WWE's thin , the decision was made to bring him back. WWE officials knew Cena would be returning 4 or ago but didn't decide on the match against Alberto Del Rio until this past weekend.
As of Monday, the plan is for Cena vs. Del Rio for the World Heavyweight Title to be a singles match, not a Hell In a Cell match.
SOURCE / CREDIT - PWInsider