Williams believe Valtteri Bottas is not a genuine rookie given last year's experience with the team.
Although Bottas will make his racing debut in Australia next month, the Finn already has some experience having contested 15 Friday practice sessions last season.
"Because he has been with us for a long time and because he has done a few Friday sessions, we know him well," Williams chief race engineer Xevi Pujolar told Autosport.
"We don't feel like he is a rookie. His feedback is good as well."
Bottas will partner Pastor Maldonado this season, the debutant teaming up with last year's Spanish GP winner in a combination that Pujolar believes will push Williams forward.
"Pastor improved a lot towards the end of last year and Bottas, when he was in the car, showed he had good performance," he added.
"If he performs this way, it will be good to have both pushing each other, and the two car crews so that there can be a competition in the team all the time that we are working together."