Gary Neville believes Arsenal manager Arsene Wenger "has got some big challenges" on his hands after signing Pierre-Emerick Aubameyang.
The Gunners signed the Gabon international on deadline day, parting with £56million to land the striker they consider to be Alexis Sanchez's replacement.
His could make his debut for Arsenal on Saturday, when the north London club play host to Everton at the Emirates, despite suffering with illness this week.
But Manchester United legend Neville fears Arsenal are now a little too top-heavy, following the signing, and perhaps in danger of being picked off by well-organised teams.
"Those four are so attacking I can't think of a defensive mind among them," said the former Red Devils defender on Sky Sports.
"I watched Mkhitaryan at United, he doesn't defend.
"Ozil, when he wants to he can, but he doesn't really want to put it in defensively. They're going to leave huge spaces.
"The situation poses Wenger a problem he will have to try and resolve on the training pitch.
"That is the problem – how do you fit all four in the same team?
"I'm not quite sure that will happen. It doesn't look like a natural fit, so Arsene Wenger has got some big challenges on the training field to make those four into a unit that works."