Per Mertesacker has challenged Arsenal to show more aggression as they look to recover from their latest European flop in Sunday's showdown with Premier League leaders Manchester United.

Arsene Wenger's side suffered an embarrassing 3-2 home defeat against Olympiakos in midweek that left them in severe danger of missing out on a place in the Champions League knock-out stages for the first time in 16 years.

Adding to the Gunners' humiliation was the horrendous blunder from goalkeeper David Ospina, who dropped a corner into his own net to gift the Greeks their second goal and in the process triggered a barrage of criticism for Wenger for his decision to rest regular first choice Petr Cech.

But Arsenal defender Mertesacker offered no excuses for his team's second successive European loss and admitted they must rediscover their fighting spirit to avoid another damaging defeat against in-form United.

"At home we should be much more aggressive from the start and be more dynamic. That is what our game is all about," Mertesacker said.

"When we play like we did (on Tuesday), with that lack of concentration and discipline, then we have got no chance.

"I think everyone will have regrets. It will take a couple of days to recover and to think about Manchester United, which will be a good opportunity to play our style of football again."

While Wenger is certain to restore Cech to his starting line-up if he is fully fit, Manchester United manager Louis van Gaal has to decide whether to make changes four days after a 2-1 Champions League victory over Wolfsburg.

United head to the Emirates Stadium, where the Gunners have won just once this season, on a four-match winning streak in all competitions which has lifted them one point clear of second placed Manchester City and three ahead of fourth placed Arsenal.

But van Gaal said immediately after the Wolfsburg game that his players were "suffering" after playing six matches in 18 days and he could be forced to freshen up the team.

"The solution is recovery," van Gaal said. "That's why it's so difficult to prepare for the match against Arsenal.

"As a manager, you want to prepare out on the training pitch, and you cannot do that because you need freshness.

"There is another solution, which is to change your squad."

- Inconsistent -

Like Arsenal, Chelsea, who host Southampton on Saturday, are also licking their wounds following a painful Champions League defeat that raised renewed questions about their lethargic form.

After watching Chelsea punished for more defensive mistakes in a 2-1 defeat at his former club Porto, Blues boss Jose Mourinho once again expressed his frustration at his players' inconsistent efforts.

But Chelsea striker Diego Costa remains confident the champions, who are languishing in 14th place following last weekend's draw with Newcastle, can still mount a successful title defence as long as they don't let the criticism get to them.    

"To come out of this we need to be all together, and for everyone to give a little more," said Costa, who played against Porto but completes his three-match ban in the Southampton fixture.

"We are not playing well, this is not a good moment, but we have players to get out of this easily."

Liverpool manager Brendan Rodgers is one of the few Premier League bosses under more pressure than Mourinho at present and Everton would dearly love to add to his worries in the 225th Merseyside derby on Sunday.

The Reds are unbeaten in their last 10 meetings with Everton in all competitions dating back to October 2010.

But an end to that run at Goodison Park this weekend would further complicate Rodgers' position after a stormy few weeks which saw Carlo Ancelotti and Jurgen Klopp linked with his job as Liverpool fell off the early pace in race to qualify for the Champions League.

And Everton's Belgium striker Romelu Lukaku is relishing the chance to make Liverpool suffer.

"The derby is a different game. It is about the personal pride and the pride for us as a club," he said.

"The side that is hungrier is going to win this game on Sunday."

Fixtures (1400 GMT unless stated)

Saturday

Aston Villa v Stoke, Bournemouth v Watford, Chelsea v Southampton (1630 GMT), Crystal Palace v West Brom (1145 GMT), Manchester City v Newcastle, Norwich v Leicester, Sunderland v West Ham

Sunday

Arsenal v Manchester United (1500 GMT), Everton v Liverpool (1230 GMT), Swansea v Tottenham (1500 GMT)
Source: AFP