Arsenal title winner Paul Merson admits he's concerned about their defence ahead of the Premier League restart.

The Gunners suffered a shock 3-2 defeat by Brentford in a practice match at the Emirates this week, with David Luiz chief among those responsible for individual howlers.

"I worry for Arsenal," Merson said on Sky Sports' The Football Show.

"I watched their goals that they let in against Brentford and I worry about them playing against closed doors.

"When you're not a great defender, and there are a few at Arsenal, I think the fans keep you honest, and I mean that in the way they keep your concentration levels.

"As defenders you need the fans there where you're always going to concentrate. I don't know if you saw one of the goals against Brentford, David Luiz tried to play out and flick it over the guy's head, that's not being honest.

"The fans keep you honest. For Arsenal it's going to be a problem defensively, because I think they'll switch off, behind closed doors, no crowd, there could be mistake after mistake."