Early reports suggest Liverpool’s top scorer suffered a hamstring strain and could be out of action for around 10 days.
"I am very disappointed about this because it now looks like we will lose Fernando for three very important games," Benitez told the Liverpool Echo.
"The initial reports say Fernando is likely to be out for around ten days and that would mean he would miss these games.
"There are too many international games and the demands on the players are too much. Someone needs to analyse this situation because it is putting the players at risk of injury.
"Maybe the answer is for there to be a two tier qualifying system because there are too many games in the qualifiers for the World Cup and the European Championships which are not competitive but which still place great demands on the players.
"These fixtures are unnecessary and maybe it would be better if the weaker countries played one another and the best of them went to play the stronger countries in the qualifiers."