BIRMINGHAM, Ala. -- WWE Champion John Cena has suffered a complete tear of his right pectoral tendon and needed surgery, according to noted orthopedic surgeon Dr. James Andrews. Because of the seriousness of the injury, WWE officials will not allow Cena to compete this Sunday at No Mercy, and he will have no choice but to surrender the title.

As a result of the injury, Cena could miss between six months to one year of action. Cena was injured during his match Monday night on Raw. According to WWE physician Dr. Ferdinand Rios, Cena's injury was more serious than initially thought.

"He has a complete tear of his pectoralus major muscle," Rios said. "Because he's so big, [the tendon tear] is behind the muscle. It was hard to diagnose."

Rios said Cena will be hospitalized for a few days to learn the rehabilitation procedure he must undergo. His arm will be immobilized for a week and then therapists may allow him to start moving it so that the arm doesn't become stiff.

Rios said that Cena is so dedicated to WWE that he wouldn't be surprised to see him return sooner than later.

"I suspect that John might be able to come back sooner [than most people with this injury], as he'll train vigorously," Rios said.

Before visiting Dr. Andrews, Cena had said last night, "No matter how serious the injury, one way or another I'll be ready to compete on Sunday."

But despite Cena's vow, WWE officials will not allow him to compete at No Mercy. Therefore, he must surrender the WWE Championship.

WWE officials vow that there will be a WWE Championship Match this Sunday at No Mercy and a new WWE Champion will be crowned.

UPDATE: WWE Chairman Mr. McMahon opened ECW on Sci Fi Tuesday night with the announcement that John Cena's injury required immediate surgery, and the now-former WWE Champion will miss six months to a year. Mr. McMahon also assured, however, that the vacant WWE Championship will not remain that way for long; at No Mercy this Sunday, a new WWE Champion will be crowned, and "history will be made."

Stay with WWE.com for further updates on Cena's condition and on No Mercy as they become available.

WATCH: Video of Cena's match on Raw

PHOTOS: Cena's injury