David Luiz tipped to 'excel' at Arsenal by Per Mertesacker
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Former Arsenal player Per Mertesacker has backed David Luiz to be a success at the club after a difficult start.

Luiz joined Arsenal from rivals Chelsea on Deadline Day for a fee of £8million.

He was brought in as an experienced presence to shore the Gunners up, but has struggled in their two biggest games so far.

A blatant pull-back on Mohamed Salah handed Liverpool a penalty through which they bagged a crucial second goal before going onto win 3-1.

And last time out in the North London Derby, Heung min-Son was able to breeze past him in the build-up to the visitors' opening goal.

But Mertesacker's faith in him has not been shaken. 

"I think he will learn from his mistakes on the pitch, but he is very comfortable being at Arsenal," the academy boss told Sky Sports.

"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."

Arsenal's 'lack of balance'

Arsenal look capable of troubling any defence with a frontline of record signing Nicolas Pepe, Pierre-Emerick Aubameyang and Alexandre Lacazette, which enjoyed its first collective outing against Spurs.

But Mertesacker has warned that their immense firepower will count for little if they cannot tighten-up. 

"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," he explained.

"It's not only about our three strikers providing an offensive threat. It is about these front three as well, leading the first front line as being a defensive unit.

"So I think we need to be cautious of that. No matter how much striking power you have got, you need to have a sense of defensive compactness from everyone."

Stats bear out concerns

Arsenal have both scored and conceded six goals so far this season, indicating that defensive frailty might well continue to restrict their progress.

Last season, they comfortably outscored top four rivals Chelsea and Spurs (73 to 63 and 67 respectively) but were undone by their poorer defensive record.

They shipped 51 goals, 12 more than their city rivals.

Unai Emery will hope that the upcoming return of Rob Holding, Hector Bellerin and summer signing Kieran Tierney brings greater solidity