The Turin giants are eight points clear of Roma at the top of Serie A heading into the halfway point of the season.
They travel to Sardinia having won their last 10 league games, including a 3-0 triumph over Roma in their first game of 2014.
"It was important to win against Roma because they are our direct rivals for the scudetto," Barzagli said. "However, the scudetto is not in our pocket.
"There are still 20 games left to play and we still have a lot of work to do.
"Eight points is a good advantage but we cannot get carried away by our current position and our good run of form.
"We have to continue to work hard and remain focused."
Juve coach Antonio Conte is expected to keep changes to the side that beat Roma to a minimum although the visitors will have to overcome the absence of Barzagli, who is suspended.
Martin Caceres is set to replace Barzagli in defence while Fernando Llorente will partner Carlos Tevez up front.
Cagliari coach Diego Lopez is aware his side will need to be at their very best if they are to end Juventus' impressive form at the Sant' Elia stadium.
Juve have shown no signs of weakness, scoring 26 goals and giving away just one in their last 10 league games.
"We know we face a very difficult game," Lopez said. "We cannot afford to make any mistakes because Juve will take no time in making us pay.
"We have to make the most of our chances and put Juve under pressure."
Cagliari go into the encounter on the back of a goalless result at Chievo, their third straight draw, and have not won since beating Genoa 2-1 on December 8.
The Islanders, who will be without injured striker Nene, have lost just once at home this season and are 12th in the standings.