Rey Mysterio was able to add the one title to his rèsumè this past Sunday that had long alluded him during his WWE days - the United States Championship.

Despite challenging for that very same belt at WrestleMania 35, he wasn't able to get the job done and he was defeated in abrupt fashion by Samoa Joe at MetLife Stadium.

The Master of the 619 was given another opportunity though to make amends at Money In The Bank, and he did just that.

In another relatively short match, Mysterio pinned Joe to win his first ever U.S. Title, despite Joe's left shoulder not being on the mat.

It turns out the match was cut short due to the bloody nature of Joe's fact, which happened due to the fact he suffered a broken nose at the hands of Mysterio.

A post-match beatdown of Rey in-front of his own son, Dominick, saw Joe prolong himself as a monster heel and look strong in the face of losing, but Mysterio seemed in genuine pain following the bout.

WWE told fans that he had suffered a shoulder injury on Raw this week, and that the state of the U.S. Championship would be addressed on next week's show.

Mysterio took to Instagram today to explain the current prognosis of his injury - a separated shoulder - and how he's recuperating.

“Due to the result at the ending of the match [at Money In The Bank] I separated a little bit of my AC joint, and we’re doing some PRP sessions here at the lab," said Mysterio.

"Hopefully, this will improve my range of motion, which has been really bad. I got two Uranage’s from Samoa Joe. Landed on my left shoulder, put all the weight on it. I’ve been having a hard time lifting up my arm.”

The fact that Mysterio doesn't look like he's undergoing surgery seems to be a positive step in regards to him not vacating the title, but there's the possibility that this method doesn't heal him.

It would be incredibly bad luck should Mysterio have to drop the title so soon after winning it for the very first time, but lets hope it doesn't get to that stage as he attempts to recover in the coming days and weeks.