Everton skipper has defensive concerns
The Toffees have won just one of six pre-season friendlies.
"At the moment it's easy for other teams to score against us, which is something that we need to eradicate," he told evertonTV.
"It's not something you can turn on like a tap next Saturday come Arsenal, and at this moment in time we're probably physically a little bit soft.
"We need to get back to the mental toughness that we showed last season. I'm sure over the next few days, and leading up to the Arsenal game we'll be working hard at that.
"We pride ourselves on our defensive solidity, and it's probably not been there this pre-season yet. We need 11 leaders out there and that's what we've had for four years since I came to the club. We've got international players out there, everyone should be taking responsibility."