Wojciech Szczesny
Wojciech Szczesny picks the ball out the back of the net following Borussia Dortmund's openerReuters

Former Arsenal striker John Hartson has called for Gunners assistant manager Steve Bould to take a greater role in addressing the club's problems in defence.

Manager Arsene Wenger and Bould watched on as their side was overwhelmed by the pace and movement of Borussia Dortmund as the Bundesliga giants eased to a 2-0 victory in their Champions League Group D clash.

With debutant Hector Bellerin filling in for the injured Mathieu Debuchy, the first choice trio of Per Mertesacker, Laurent Koscielny and Kieran Gibbs were troubled throughout the evening, with little protection from their options in midfield.

Hartson, speaking to Radio 5 Live, aired his displeasure over the "unacceptable" performance of his former side and suggested his former teammate Bould would have been left "cringing" at the manner in which the Gunners' back four capitulated.

"I think Arsenal papered over the cracks last season, winning the FA Cup and just sneaking into the top four," Hartson said.

"Their performances against the big teams in the last few years have been unacceptable. They could have conceded five or six tonight.

"And the thing is, they do still create chances because they have such quality in the middle of the park. Arsenal have got good players but they need to strengthen defensively.

"Without overreacting, it was a really woeful defensive performance from Arsenal tonight.

"Steve Bould has been given the assistant manager role and he should be going in there and sorting it out at the back. He must be looking at his side's defending and cringing."

Wenger was handed another blow during the defeat after Jack Wilshere suffered an ankle injury.

The club are yet to confirm the severity of the knock but Wenger is wary given the midfielder's ankle troubles throughout his young career.

"Jack Wilshere has turned his ankle," he said. "It is difficult to say how bad it is because I am a bit cautious. Normally it is not very bad but because of his history I am a bit cautious. Apart from that, no player I took off was injured."