Ronald Koeman demands his Everton players stand up and arrest slump in results as they prepare for Man United trip and reunion with Romelu Lukaku

• e-mail

Ronald Koeman has called a summit meeting with Everton's players to demand an explanation for the reason their alarming loss of form.

Everton's squad arrived back on Merseyside in the early hours of Friday morning after being blitzed by Atalanta in their first Europa League group game.

It was their second 3-0 defeat in the space of five days and the spineless manner of the performance has left Koeman 'worried'.

Everton manager Ronald Koeman has demanded a response from his players when they visit Manchester United in the Premier League on Sunday

The Dutchman was left fuming as Everton lost 3-0 to Atalanta in the Europa League

Having spent £135million during the summer, Koeman is aware there is a pressure on him to get results and take Everton forward and, in what was a candid press conference, he did not try to offer any excuses for a run of five games without a win in all competitions.

What was also clear, though, was the fact Koeman will not tolerate the slipping of standards and the focus on the meeting at Finch Farm, Everton's training base, will be to remind the senior members of his group of their responsibilities to help end this slide.

'I will have a meeting with most of the players – with the key players,' said Koeman, whose side travel to Old Trafford on Sunday for a reunion with Romelu Lukaku.

'A young talent of 18 or 19? Ok. But it's time for the experienced players to stand up.

Wayne Rooney expresses his frustration during Thursday's 3-0 defeat in Italy

A dejected Gylfi Sigurdsson after Everton concede a goal in their Europa League defeat

'I am worried about what I saw yesterday. I wasn't so worried after Chelsea. It (his worries) start already with the reaction in the second half against Tottenham. That 45 minutes and the first 45 minutes of yesterday are enough reason to be worried.

'I saw a team with a lot of doubts. One of our strengths last season was that we had good defensive organisation and now we have lost our strength. It was painful. 

'They showed more ambition, more aggression and in the way they defend, so close and tight. There was a big difference.'

Everton have not kept a clean sheet since the opening day, when they beat Stoke City 1-0, and Koeman fears that if they continue to be so passive and lacking fight, Lukaku – who joined Manchester United for £90million in June – will run amok.

'We know him really well,' said Koeman. 'He's one of the best strikers and I said several times last season he is a real finisher. I know how we have to defend him. 

'He is dangerous in the box and fast and strong. If we are defending how we defend in the last few games it will be his afternoon.'

Atalanta's Alejandro Gomez celebrates his goal on a comfortable night for the Serie A team

Everton are set for a reunion with in-form United striker Romelu Lukaku on Sunday

The other concern for Koeman is that his side have been incapable of scoring. 

Nobody other than Wayne Rooney has scored for Everton in the Premier League but the manager is refusing to blame the drought on them failing to sign a striker in the window – Olivier Giroud was his preferred choice.

'It's not now the frustration because you cannot do anything at this time,' said Koeman, who also wanted to try to bring Diego Costa to the club on loan. 

'If you have a target man in front? You saw Atalanta, the striker kept the ball when it went up him and the team keeps the ball.

'We have different types in Dominic (Calvert-Lewin) and Sandro (Ramirez). Dominic needs time and Sandro needs to adapt to the Premier League. Yes he has pace. But it's too easy to mention the strikers because we make a lot of mistakes.'