Alessio felt they failed to play as a unit in the 1-0 reverse.
"When we do not play as a team unit, then we suffer and lose in this way," he said.
"There was some fatigue after the Chelsea match, even if in certain games the energy and motivation come by themselves."
The game was decided by an extremely dubious Robinho penalty, as replays show the ball struck Mauricio Isla on the ribs rather than the arm.
"I daren't imagine what would've happened if we had won with a penalty like that, but incidents can happen."