The youngster has not been involved for the Gunners in recent weeks.
His manager stated a few days ago that Martinelli had to work harder in training and in games.
But he backed the talented striker after a 3-1 win over Leicester City on Sunday.
Asked about Martinelli, he told reporters: "Well, he needs to keep working and making it difficult for us.
"He is a player that is going to give us a lot, but we need some time to find the right games for him and the right connections with him on the pitch so that he can do what he does best.
"But the way he is and the way he trains every day, he is going to be a really important player for us, no doubt.
"But when you have many options, it is difficult when you look for certain qualities in certain games."
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