The Serie A leaders have failed to win their last three matches in all competitions, the latest a 1-1 draw with Sampdoria on Sunday.
Manolo Gabbiadini's strike ensured Juve dropped points for the second successive week and allowed Roma to close the gap at the top to just one point.
Juve travel to Sardinia with the hosts in the bottom three and Allegri has called for full concentration to get back on track before the mid-season break.
He said: "We expect a difficult game. They're in need of points to stay up and have plenty to offer up front.
"We need to get back to winnings ways by turning in a great performance.
"Cagliari always play an open game and we'll be in for an entertaining encounter. We've done well so far but have the quality to do even better."
It remains to be seen whether Allegri will be on the touchline for the match, though, after receiving a one-match ban for using insulting language towards a match official against Sampdoria.
The 47-year-old has appealed the decision and admits he was surprised to be hit with such a sanction.
"I am surprised by my touchline ban," he added.
"I'm no saint, but I'd say my behaviour towards match officials has always been decent."
