Rey Mysterio is said to be legitimately injured and out of action.
As noted earlier, WWE announced during RAW that Mysterio suffered a torn triceps during the win with son Dominik Mysterio over Seth Rollins and Murphy at Sunday's WWE Payback pay-per-view. Rey was pulled from his singles match with Rollins on this week's RAW, and replaced by Dominik, but there had been some speculation on this being another storyline injury for Rey.
In an update, Dave Meltzer of F4Wonline.com reports that the injury to Rey is legitimate, and did occur during the tag team match at Payback on Sunday night.
While WWE is calling the injury a triceps tear, and that's likely exactly what it is, it is not thought to be as serious as a full tear, which would require surgery.
Word going around Monday's RAW was that Mysterio is expected to be out of action for two months, or maybe less. He will reportedly be able to recover through rehab, and reportedly will not need surgery.
Rey appeared in a backstage segment on Monday's RAW with his wife, daughter and son, and was wearing a sleeve over part of his arm, but no sling.
Rey recently signed what is believed to be a new three-year WWE contract. Stay tuned for updates on his status.