"We are really happy with Robbie and he is working hard, but you need to know exactly how many top class strikers you need to win trophies or if Robbie is that type of top class striker," said Benitez.
"There is no doubt that Robbie is a top class player, but you also need qualities in the team like pace and stamina if you want to win trophies.
"If you have a player like Robbie then you have no doubts about his qualities, but you need to know what his performances will be like all season.
"It is not easy to find better players than Robbie. And it is difficult to find anyone with the passion he has for the club. But maybe you could find three top class strikers who are 23 years old and can score goals and have pace and then you have to think.
"There's no problem with Robbie. I have been talking to him and we are not in a hurry, and he knows why. Robbie knows he needs to improve and in which areas. He understands the situation.
"He knows that we need to decide in maybe three weeks or a month, and he needs to continue to work hard but we know he is a good finisher and a good player. But we need to know how he will play next season and what level his physical condition will allow him to play at."