The Gunners signed the 19-year-old defender last summer from Saint-Etienne for a fee of £27million.
“I think William is doing really well," the Spaniard said of Saliba. "He is adapting to the country, adapting to our club.
“We have to bear in mind that he had a really challenging season last year with the amount of injuries that he had.
“But he is a player that is going to be really important in our future, things sometimes take some time and we have to respect that."