CESC Fabregas has warned free-scoring Arsenal cannot afford to make costly mistakes at the back if the Gunners are to become genuine challengers for the Barclays Premier League title.

Arsene Wenger’s side swept past Champions League new boys Braga 6-0 on Wednesday night, taking their goals tally to 16 in just three matches at the Emirates Stadium.

Arsenal head to Sunderland this evening, where they lost 1-0 last November, and are expected to face another stern test of their championship credentials.

While there is no doubt the Gunners are awesome in attack at their free-flowing best, question marks remain over consistency in defence.

With Thomas Vermaelen battling to recover from an Achilles problem which has seen him miss the last two matches, new recruits Laurent Koscielny and Sebastien Squillaci are likely again to be partnered in central defence.

The Frenchmen performed well under the stresses of Bolton’s physical approach last week, but were caught out when a weak back header from Koscielny allowed the visitors to set up an equaliser.

While Arsenal went on to win the match comfortably, Fabregas knows it could have proved a costly error.

“We made a mistake at the back towards the end of the first half and were punished – we cannot afford to do that at this level, and it shows there are still things to improve on,” said the Gunners captain.

Arsenal reported no fresh injury problems following Wednesday night’s comfortable victory.

However, Wenger is conscious of the demands on his players, and so could shuffle things around, as he did for the last league game against Bolton, so winger Tomas Rosicky and England fullback Kieran Gibbs could be involved having been unused substitutes in midweek, while Mexican forward Carlos Vela made an impression with a late brace after coming off the bench.

Arsene Wenger admits he was impressed by the efforts of Sunderland’s Asamoah Gyan this summer.

“I looked at him especially during the World Cup,” the Arsenal manager said.

“He had spells at Rennes last year where he didn’t play and some periods where he was absolutely outstanding.

“When I saw him at the World Cup I found him extremely interesting and a good player, but at the time we already had our strikers so I was not looking for him.”