Benitez, whose side remain unbeaten in the league this season, said: "We have a lot of games to play in December and January, so you never know at this stage where we will be. We could have some problems - today Jack Hobbs needed to play - so we need to keep the squad focused."
Hobbs, the 19-year-old central defender signed from Lincoln City in 2005, was required to rise from the bench after Jamie Carragher sustained a second rib injury of the season in a collision with his own goalkeeper Jose Reina.
"It is not serious," said Benitez. "Normally he should be fit for next weekend's game but we will have to wait."