Tuesday's Champions League match between Barcelona and Atlético Madrid at Camp Nou is turning into a bloodbath. Gerard Piqué went off injured early in the match and the man who contributed to that injury, Diego Costa, has now joined him on the sidelines. He pulled up lame in the 28th minute, apparently injuring his hamstring, and was subbed off.
Diego Simeone replaced Costa with Diego, an attacking midfielder, so Atlético Madrid are changing formations as a result of the injury. Diego should slot in behind David Villa.
Costa was questionable for the match because of an injury that he sustained in training, but Simeone said that he would be fit to start, then played him. However, that injury was believed to be to Costa's knee, while Tuesday's injury appeared to be his hamstring, so it's probably unrelated.
If Costa has to miss the second leg, there will be a lot of pressure on Villa to pick up some of the slack and turn into more of a defensive forward, something he hasn't done much of in his career.