David Luiz is not Arsenal’s “answer to their prayers”, says Martin Keown, with an unnecessary gamble being taken on a player who will be “exposed” in a much-criticised defensive unit.The Gunners have sought to build for the future at the heart of their back four by agreeing a deal for William Saliba, but have allowed him to spend the 2019-20 campaign back on loan at Saint-Etienne.Unai Emery is therefore eager to find an experienced addition to his ranks for the current campaign, with Laurent Koscielny having forced through a switch to Bordeaux. Article continues below Editors’ Picks Emery out of jail – for now – as brilliant Pepe papers over Arsenal’s cracks What is Manchester United’s ownership situation and how would Kevin Glazer’s sale of shares affect the club? Ox-rated! Dream night in Genk for Liverpool ace after injury nightmare Messi a man for all Champions League seasons – but will this really be Barcelona’s? Chelsea star Luiz is the man Arsenal have set their sights on, with Goal able to confirm that an £8 million ($10m) agreement is in place, but Keown has questioned the logic of swooping for the 32-year-old Brazil international.The former Gunners centre-half told the Daily Mail: “Yes, Arsenal want a centre back, but is Luiz the answer to their prayers? I don’t think so. “The way the 32-year-old plays, he would be exposed in that Arsenal defence. He would not get the same protection that he enjoys at Chelsea, where N’Golo Kante patrols in front of the back line. “In possession, Luiz is a wonderful passer, but he makes mistakes when playing as part of a back four.“He has a tendency to lose his marker and is one of those all-or-nothing players — if he doesn’t win the ball in a challenge, then congratulations because you’re in. “Luiz is clearly a big personality. Maybe Emery thinks he can control the Brazilian — they crossed paths at Paris Saint-Germain — but him missing first-team training with Chelsea on Wednesday is a red flag. “Let’s not forget that Arsenal have just been forced to sell a player to Bordeaux who did this to them.“Laurent Koscielny was club captain and always came across as a good egg, but he still made sure he got his move. “He refused to take part in their pre-season tour of the United States. That proved how even the most well-balanced player is prepared to rock the boat in a bid to get his way. “Do Arsenal really want to be on the receiving end of someone willing to kick up a similar fuss now? That’s why I question whether he (Luiz) would be suitable for Emery.”If Arsenal do push through a deal for Luiz, and Celtic left-back Kieran Tierney, then it could be that Emery fields a new-look line up in a Premier League opener against Newcastle on Sunday.The Gunners have already broken their transfer record this summer to acquire £72m ($88m) forward Nicolas Pepe, while also taking midfielder Dani Ceballos on loan from Real Madrid and exciting teenager Gabriel Martinelli from Ituano.