Appears that Sami Zayn did suffer some sort of arm/shoulder injury during his awesome main roster debut against John Cena, landing funny on a Cena back suplex. Zayn continued working the match after a brief respite to let the trainer attend to him, and in all the match went roughly 11 minutes. Zayn was noticeably favoring the arm in the match's later stages, and since Cena didn't go to exploit the injury, it's apparent that he wasn't selling. Zayn did manage to hit his torpedo DDT with said arm (the left one) so it's not as if his range of motion was compromised.
Hopefully the MRI shows no significant damage, as Zayn made his first big break on the main stage count in one hell of a frenzied match against Cena. The sky really is the limit for him.
UPDATE: Wrestling Observer is reporting that, strangely enough, Zayn apparently injured his arm/shoulder while rallying the fans prior to the beginning of his match with Cena. He'd previously been in and out of action for the past month. Guess the Cena-hating mob can put down the pitchforks and not cry conspiracy.