The Terriers, who hovered in and around the play-off places during the first four months of the season, have failed to win any of their last 12 league matches and are now seven points clear of the relegation zone in 18th place.
"The only thing that will get us out of our current predicament is hard work," said Grayson after his side's 4-0 defeat at Watford on Saturday.
"If that means doing double training sessions and for some players to lose their shirt, then we will have to do that.
"If you don't work harder than the opposition then you will get punished. We aren't covering the distances with any sort of desire."
Grayson was particularly concerned at the manner of his side's defeat at the weekend.
"It is hugely disappointing for everyone involved with the football club and most importantly the fans that have travelled all this way," he added.
"The players are making individual errors; their second goal is a good example of that.
"It was too easy for them to cross the ball in to the box. We didn't work hard enough to shut the Watford player down. Also, for the third goal, the two defenders have made bad errors which allowed their striker through on goal.
"When the second and third goals went in we started feeling sorry for ourselves. Teams are ruthless in the Championship and if you give them half a yard they will stamp all over you."