Liverpool striker Fernando Torres is a doubt for the visit of West Ham.
The Spain international missed last weekend's goalless draw against Fulham after flying to Barcelona to have a knee injury assessed by a specialist.
Having returned to Merseyside for the Hillsborough memorial service, he was due to fly out to Spain for another examination by the surgeon who operated on the knee in January but the closure of British airspace for the volcanic ash cloud has delayed that.
Benitez will not consider playing Torres until he has had another examination, which puts his participation against West Ham in doubt.
Defenders Emiliano Insua and Fabio Aurelio are still out so Daniel Agger is set to continue at left-back.