#3 - Finn Bálor tears his labrum (2016)

An internationally-acclaimed superstar and one of NXT's biggest signings/success stories, Finn Bálor was an obvious choice for a main-event talent on the WWE roster.
He made an immediate impact upon his Monday Night RAW debut in July of 2016, winning a Fatal-4-Way with Rusev, Cesaro, and Kevin Owens, then defeating Roman Reigns (clean!) in that night's main event. And with those victories, the match was set - it would be "The Demon King" Finn Bálor versus Seth Rollins at SummerSlam for the newly-minted WWE Universal Championship.
Did you know a top WWE Superstar just wrestled outside the company? More details HERE
Throughout the second half of the match, it was clear that something was wrong.
After taking a Release Powerbomb onto the barricade from Rollins, Bálor was in visible distress. It seemed as if he was making a conscious effort to keep his arm (the one he used to try to break his fall against the barricade earlier) from moving. Nevertheless, Bálor soldiered on and won the match, becoming the first ever WWE Universal Champion.
The next night, he was forced to vacate his title, as an MRI revealed that he had torn his labrum and would require surgery. The injury would keep him on the shelf for six months, and since his return to the main roster in April of this year, he has yet to receive his one-on-one rematch for the title that he never lost.