I'm not a doctor, but did stay in a Holiday Inn Express last night...
From the reports prior to and after the procedure, it seems more than likely E.J. Manuel's procedure was a PRP injection (link below). By now E.J.3 should be stretching and strengthening the knee and should be back on the field as early as next week.
http://www.hss.edu/condition-list_prp-injections.asp