Newcastle have signed Hanley from Blackburn Rovers, and the centre-back is expected to have a key role to play over the season ahead.
The Scotland international is widely anticipated to be part of Newcastle’s starting line-up.
However, Benitez opted against including Hanley in his Newcastle squad which faced Sporting Lokeren yesterday.
And the Spanish boss said: “Grant Hanley has just arrived and he needs to improve his fitness.
“He has been some time without training with the team properly.”
Newcastle’s next friendly comes against Southend United on Tuesday night, where Hanley could make his first appearance.
In Hanley’s absence, Benitez’s side still put in a thoroughly accomplished performance against Lokeren and ran out 4-0 winners.
A brace from Ayoze Perez and strikes from Daryl Janmaat and Jonjo Shelvey provided Newcastle with a comfortable victory.
The Tynesiders’ competitive campaign gets underway with a match against Fulham at Craven Cottage next month.