United have made their worst start to a league campaign for 17 years after collecting just 20 points from their opening 13 matches.
Sunday's frustrating 1-1 draw with West Ham at Old Trafford was a fourth consecutive home league stalemate, a sequence United have not endured the like of since 1980.
But with Hammers goalkeeper Darren Randolph a clear man of the match after making a series of outstanding saves, and after similar experiences against other opponents, midfielder Herrera is convinced United are doing little wrong.
The Spaniard said: "I don't know what to say. At the moment, luck is completely against us.