Martinelli, 18, joined the Gunners in July from Ituano in his homeland of Brazil.
The forward is more of a peripheral player at the moment but has impressed whenever he’s been given a chance in the first-team.
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In the two games he’s started this season, Martinelli has scored four goals – a 4-0 win over Standard Liege in the Europa League and a 5-0 triumph over Nottingham Forest in the Carabao Cup.
If Martinelli carries on as he is, it surely won’t be long before manager Unai Emery considers him for a more regular spot in the first-team.
And Holding lifted the lid on Martinelli’s relentless work-ethic in training, claiming he is a ‘nightmare’ for centre-backs.
Holding said: “He’s [Martinelli] come in and settled really well.
“In training every day, he works hard. He puts you under pressure constantly and never stops running, which as a centre half is a nightmare. You want a striker that will sort of give up on you, but he never gives up.
“His finishing has been unbelievable, even with his head. He’s only a small guy but the headed goals he’s scored in the Forest game and the Standard Liege game have been incredible goals, to be fair to him.”
The defender also revealed that Martinelli is working on his English all the time and is actually using a yoga class to help him achieve this.
Holding added: “I think he’s really close with Emi [Emiliano] Martinez.