Saturday's 3-1 defeat by Sheffield Wednesday means the Bluebirds have won only one game out of their last six.
"We're not working hard enough as a team or playing to our strengths," said striker Chopra.
"At Sheffield Wednesday, we weren't winning tackles or headers."
There is better news off the pitch, however, after Cardiff secured a new shirt-sponsorship deal with online betting firm SBOBET, believed to be worth £250,000.
Source: Team_Talk