Barzagli arrived in the winter market from Wolfsburg.
He said: "It will be a big game. Inter went through a difficult period at the start of the season, but they have rediscovered their best form since the arrival of Leonardo and are back in the title race.
"Sunday's match will be open. It's very important for both teams. Inter will be looking to stay in the title race, but we must give continuity to our win in Cagliari."