This was confirmed by TMZ Sports: "Sting would have decided to retire after receiving several unfavorable diagnoses of the injury he suffered at Night of Champions in the fight against Seth Rollins."
It is worth noting that it is the same injury that caused Edge to retire in 2011. However, Sting has not yet commented on the matter, but it is almost certain that the 'Icon' will hang up his boots in the WWE.
But it is presumed that Sting will make the official announcement on April 2, one day before Wrestlemania 32, when he is inducted into the WWE Hall of Fame. A great one is leaving!