Thomas Vermaelen has urged Barcelona not to underestimate his former Arsenal team-mates when the sides conclude their Champions League last-16 tie at Camp Nou on Wednesday.
Holders Barca secured a 2-0 advantage during the closing stages of a keenly contested match at Emirates Stadium three weeks ago, with Lionel Messi netting a late brace.
Luis Enrique's men are chasing their 10th consecutive home win in Europe's premier competition but, despite the fact Arsenal appear to be on course to once again miss out on a quarter-final berth they were last able to claim in 2010, Vermaelen is taking nothing for granted.
"It won't be an easy game at all," the Belgium defender, who swapped north London for Catalonia in August 2014, told Barcelona's official website.
"Although we have a small lead, you can never say that they are out. They have very quick players and that makes them dangerous. We'll need to concentrate.
"It is two different team [who are] very similar in the way they play. They look to play a passing game and keep the ball on the ground. They don't go for long balls.
"It would be incredible to win [the Champions League] again but there's still a long way to go. There are lots of games left and we'll have to work hard if we want to do it."
While Barca are sitting pretty at the top of La Liga, Arsenal's Premier League title challenge has floundered on the back of three winless outings.
The pressure on long-serving manager Arsene Wenger was further increased by a shock FA Cup quarter-final defeat to Watford on Sunday.
Per Mertesacker underlined the fine margins Arsenal must hit on Tuesday - bemoaning a tension that undermined their work against Watford before warning that there is no margin for error at Camp Nou.
"We were not relaxed against Watford. Even in the box we played and always found good positions, with the man in the right position but we lacked that relaxation even to hit the target," the centre-back told his club's official website. "We did not do that sometimes. We missed it too often.
"We cannot afford to concede against Barcelona. We have to go there and try to attack, no matter what, that is the only possibility we have. We can be fortunate to have such big game in front of us.
"They are the ultimate team at the minute, so we are straight away under pressure and we have to go away from home. I think the confidence is there, we are just missing something.
"The season is not over. We play in a confident way, we maybe lack that bit at the end. The desire to play together and to be good as a team is there, you can feel that."
The task for Mertesacker and his defensive colleagues will be made more difficult by Luis Suarez's expected return to the Barcelona starting line-up - the Uruguay striker having rested as his colleagues routed Getafe 6-0 on Saturday.
Danny Welbeck and Theo Walcott provide options for Wenger to bolster his attack with pace in search of the goals required, the former having come off the bench to net a late consolation as Watford held on for a 2-1 win.
Key Opta stats:
- Barcelona have won the Champions League in four of the last 10 seasons and are aiming to be the first team to retain the European title since AC Milan in 1990.
- Arsenal lost knockout encounters against Barcelona in 2009-10 and 2010-11 after also falling short in the 2006 final.
- Arsene Wenger's side have conceded seven goals on their previous two trips to the Camp Nou.
- Barcelona are one of two unbeaten teams remaining in the Champions League this season, along with rivals Real Madrid.
- Lionel Messi, Luis Suarez and Neymar have scored 39 of Barcelona's 48 goals in the Champions League since the start of last season.
