Arsenal academy chief Per Mertsesacker says they're pleased with summer signing David Luiz.

Luiz joined Arsenal on the final day of the English transfer window from Chelsea for a cut-price of £8million.

During Liverpool's 3-1 loss to Arsenal earlier this season, Luiz was arguably at fault for two of the Reds' goals.

"I think he (David Luiz) will learn from his mistakes on the pitch, but he is very comfortable being at Arsenal," he said.

"That's what I have been seeing. So we are happy to have him.

"He brings something different to the table right now. So I think he is able to learn and excel his level of being an Arsenal player.

"I think we have a lack of balance right now. Where you feel like, ok we have amazing strikers but they as well need to understand that we need to have a certain compactness."