As reported by CalcioMercato, Danish captain and Milan defender Simon Kjaer exited the round of 16 victory against Wales due to a muscle problem. The defender went to the turf in the 77th minute of Denmark's 4-0 victory and could not carry on. The injury was reported as a "muscle problem in his right thigh". No tests have been done thus far, and Denmark will monitor the situation.
Kjaer has suffered injuries this season with Milan, so this does not come as shocking news to fans. Hopefully the injury is benign and the captain can resume play for his club in the next round.