The Gunners have had an explosive start to the new season with seven wins and one draw.
But Old Trafford defender Evra believes there could be a fragility beneath.
The French left-back said: "There is no doubt that Arsenal are a stronger side than they were last season.
"But I don't think we will know about this Arsenal team this season until they lose.
"That's the important time when you look to see how a team reacts. It is how you bounce back.
"We know we can do it. We had a difficult start to the season but we have shown great strength and character and are winning now without conceding any goals."
While the season is not yet a quarter over, Evra believes the champions are already looking better than last term.
He added: "We are stronger throughout the team than last season.
"At the end of last season we were struggling with injuries and that was one of the reasons we lost in the semi-finals of the Champions League.
"I think we have the strength not only to win the league this season but do better in that competition."