Knockaert has been targeted by Newcastle, as they look to add new players before the season starts.
The Magpies have already had one offered turned down for the skilful winger.
And Benitez said: “We know that will not be easy. We are rivals and I think it will be tough to convince them.
“Normally you try and, if you cannot, you have to move on and start thinking about other targets.
“We will see but I think it will be difficult.”
Knockaert is considered one of Brighton’s star players, and he is valued highly by the south coast club.
The former Leicester City man only arrived at the AMEX Stadium last January, but he has made a big impression in a short amount of time.
Newcastle may be finding it difficult to complete a transfer, but Rafael Benitez has got almost every other target he has wanted this summer.
Newcastle have made seven signing so far this transfer window, with Ciaran Clark and Mo Diame the latest to sign up at St. James’ Park.