West Ham manager Gianfranco Zola believes Liverpool have paid the price this season for relying too much on Fernando Torres and Steven Gerrard.
Both players have spent time in the treatment room and the Reds have suffered as a result by fading from the race for a Champions League place.
The Hammers travel to Anfield on Monday night knowing that Torres remains a major doubt because of a knee injury and Zola offers a simple explanation for Liverpool's problems this season.
Liverpool v West Ham Utd: Video Preview
"Gerrard and Torres are massive players, when they are on the pitch it makes a big difference to Liverpool," he said.
"It's a pity they haven't been available for the whole season because of injuries and Liverpool's problems lie within that.
"Liverpool don't have the same number of players as Manchester United, Manchester City or Chelsea.
"When they are in good form they can be a really good team. They can stand with United and Chelsea.
"But Torres has had too many injuries and it's a big ask for them without him."
Zola insists Liverpool, who are scheduled to play the first leg of their Europa League semi-final against Atletico Madrid on Thursday, remain dangerous even without Torres.
"Liverpool can still cause us problems. Torres is a big asset but I like David Ngog, he can be a problem for us," he said.
"We don't have to think about Torres' injury being an advantage for us, we still need to perform and do very well."
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