The big defender was talking straight after Saturday's disappointing 3-0 home defeat against Middlesbrough in the Premiership.
Boss Glenn Hoddle described the performance as the worst in his time in charge as goals from Massimo Maccarone, Geremi and Joseph-Desire Job secured the points for the visitors.
Now comes the test of character as Second Division leaders Cardiff, conquerers of Leeds United in the FA Cup last season, arrived at the Lane for the Worthington Cup second round encounter.
"It's a big, big game for us," insisted Dean. "They are one team we can't underestimate and will be a tough side to beat. They'll bring great support with them and we'll have to stand up and be counted."
As for Saturday, a dejected Dean reflected: "It's not quite sunk in yet what went wrong.
"Maybe we approached the game in the wrong manner, underestimated them a little, perhaps thought we would take the game to them and they caught us by surprise and brought the game to us.
"We were bad from start to finish. We never got going, didn't pass the ball, gave stupid little passes away, it was disappointing. It's hard to make excuses for a performance like that."
Dean Richards says we'll have to 'stand up and be counted' against Cardiff City in the Worthington Cup on Tuesday night.