The Spain striker was taken off the pitch after only 22 minutes during his country's 1-0 win over France in a friendly on Wednesday.
"The news we have on Torres is that it is a hamstring injury. I need to talk to the doctor but I think he will miss this game," Benitez told Liverpool's official site on Thursday.
"Normally, it is a week when a player goes off like this. It is a big problem for us."
Torres appeared to be holding the back of his leg after a challenge with France's Lillian Thuram, but he played down injury fears, as he ensured that he demanded a substitution in order to catch the Sunday game.
"I preferred not to risk it, I demanded the change," he was quoted as saying by Sky Sports.
"I will have medical tests, but I intend to play on Sunday against Chelsea."
Spain doctor Jorge Candel has also claimed that 'the injury of Torres is not of major importance'.