Juventus have a perfect defensive record in Serie A with six clean sheets but the second-placed side have injuries to contend with after key players were sidelined ahead of Cagliari's visit on Sunday.Thiago Motta's side have not conceded a goal yet in six rounds but that could change with centre back Gleison Bremer - a pivotal figure in Juve's defence and the only player to play every minute so far - potentially out for the season.Cagliari, 16th with five points, may not prove the sternest of tests, but in the long run, Motta will need a replacement with the Brazilian going under the knife after injuring his anterior cruciate ligament.The centre back, who leads the team in tackles, interceptions and clearances, was forced off six minutes into their Champions League encounter with RB Leipzig following a challenge from Lois Openda.To make matters worse for Motta, winger Nico Gonzalez also went off with a thigh muscle injury in the same game.The seventh round of Serie A kicks off on Friday with Antonio Conte's Napoli taking on Como at home.Having faced his former player Motta last month, Conte will come face-to-face with another player he coached in Cesc Fabregas, Como's manager who won a Premier League title and the FA Cup under the Italian at Chelsea.After a winless start to the season, Como have turned things around with two victories on the trot to move up to 10th but unlike Juve, their defensive frailties have been exposed and they have yet to keep a clean sheet.SECOND-WORST DEFENSIVE RECORDFabregas's side have conceded 11 goals in their first six matches - the joint second-worst record in the league behind Atalanta and Parma with 12 each."We can't keep conceding two goals in every match, so we should keep analysing