Theo Walcott has urged Arsenal to ensure tomorrow's game at Wolverhampton Wanderers is not another missed opportunity to cut the gap to Chelsea at the top of the Premier League.

The Gunners suffered a surprise 1-0 home defeat to Newcastle on Sunday before watching Chelsea lose 2-0 at Liverpool, the second time this season Arsene Wenger's men have failed to capitalise on a slip-up from the champions.

Chelsea lost 1-0 at Manchester City back in September only for Arsenal to go down hours later to a shock defeat at the Emirates Stadium to promoted West Brom. The north Londoners would be top of the table had they won both those games and England forward Walcott knows they must take full advantage of Chelsea's next slip-up.

That could happen tomorrow, with the Blues hosting Fulham in the west London derby, while Arsenal travel to Molineux in matches that both kick-off at 7.45pm.

"We are still in the same position as we were before, which is five points behind Chelsea," said Walcott. "Nothing has really changed, although it was another opportunity we could have taken."

Wolves are currently second-bottom of the table but have actually performed well in the midst of a nightmare run of league and cup fixtures, including two trips to Manchester United and one to Chelsea, as well as a home clash with Manchester City. They managed to beat City along the way and Walcott is taking nothing for granted.

Theo Walcott, Arsenal forward">

(Wolves') fans will give them an extra man, but if we can get the ball down, play our football and get the early goal, then hopefully it will be a good time for us.

"Wolves have been fairly strong at home and very good away from home," he said. "Their fans will give them an extra man, but if we can get the ball down, play our football and get the early goal, then hopefully it will be a good time for us."

Arsenal romped to a 4-1 win at Molineux last season but needed a stoppage-time goal to beat them in the reverse fixture as Wolves adapted to life back in the Premier League.

Gunners boss Arsene Wenger told Arsenal TV Online: "Wolves are a side which everybody respects because, before you go there, you know they will give you a tough game with full commitment. They play good football and, for anybody to go to Wolves, it is a difficult game."

Arsenal will be without Laurent Koscielny, who today saw his appeal against his dismissal against Newcastle rejected. The defender will serve a two-match ban, ruling him out tomorrow and for Sunday's away game against Everton.

The Gunners will hope captain Cesc Fabregas is able to play through an "annoying" hamstring problem, which the midfielder has confirmed is not torn but is proving alarmingly persistent.

Wenger must also decide whether to include Robin van Persie among his substitutes after conceding the Holland striker was not ready to return despite making his first appearance since August from the bench against Newcastle.

Goalkeeper Manuel Almunia is closing in on full match-fitness following his elbow injury, and given the indecision of stand-in Lukasz Fabianski on Sunday that led to Andy Carroll's winner, the veteran Spaniard could come straight back into the side.

Russian winger Andrey Arshavin will be hoping to start at Molineux after he looked sharp as a second-half substitute against Newcastle, but midfielder Samir Nasri is a doubt.

Wenger confirmed today Nasri would be fine for tomorrow's game but had bad news on long-term absentee Thomas Vermaelen.

The Gunners boss revealed on Friday Vermaelen had been only "days" from returning to the first-team squad after more than two months out. But he damaged his Achilles again in training on Monday and will be sent back to see a specialist.

Wenger said: "I don't know where we go with Thomas time-wise but, at the moment, he cannot play. On the scan, his Achilles is completely clear but as soon as he stays out for a while, it tightens up and he has pain. We don't know the source of his pain."

Wenger also revealed midfielder Abou Diaby faces a test on his injured ankle later this week. "He has a test Wednesday or Thursday," he said. "If he gets through that, it will be very quick; if he still has pain, he will have to see a specialist."