Sunday's 4-0 loss to United was Everton's third league defeat on the trot with the 3-0 humbling at the hands of Italy's Atalanta in the Europa League last week adding to their woes.
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Sigurdsson, who arrived in the close season along with a host of new recruits as the club spent £145 million, said there were signs the squad was gelling.
"It is hard to say that after a 4-0 loss but we will stay together, stay positive and keep working," said Sigurdsson while talking to club's official website. "Even though we conceded four goals I think we were more solid as a team and harder to break down. But we are going to have to improve for the next few games."
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Everton, 18th in the league table with four points from five games, host Sunderland in the League Cup on Wednesday before Saturday's league match against Bournemouth at Goodison Park.
"A lot of us have been in this kind of position before - where things are not going your way," said Sigurdsson. "It does not look too good at the moment but I know we are more than good enough to turn this around."
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