Gerrard reported for duty on Sunday night despite the Liverpool website stating he would be unavailable after picking up a groin injury at Bolton on Saturday.
But a check by the FA's medical staff has proved that diagnosis to be correct and Gerrard has returned to the north-west.
Gerrard's midfield partner Lampard also misses out after scans on a rib injury he picked up at West Brom on Saturday revealed he would not be fit enough to be involved at the Olympic Stadium.
Benitez said: "We had to do a scan after the Bolton game because Steven said he had some pain in his groin.
"It is not a massive problem and we hope he will be ready to return in seven to 10 days."