Lionel Messi on a roll as Barcelona faces Celtic

With Lionel Messi running rampant in attack, Barcelona must tighten its leaky defense against Celtic knowing a win on Tuesday will give it total control of Group G in the Champions League.Messi scored his club record 21st career hat trick in Barcelonas wild 5-4 victory at Deportivo La Coruna on Saturday, which kept it at the top of the Spanish league alongside Atletico Madrid.But its been a decade since the Catalan team last conceded 11 league goals through the first eight rounds, and Celtic will look to exploit the vulnerability at the Camp Nou after coming off a win at Spartak Moscow.Spartak hosts Benfica in the other group match, and the Portuguese club is already facing a must-win scenario after taking only one point from its opening two games.Barcelona is hopeful center back Gerard Pique will return from a foot injury with Carles Puyol sidelined and makeshift pair Alex Song and Javier Mascherano unconvincing in a league victory that maintained Barcelonas unbeaten start to the season.Pique didnt train on Monday, while Dani Alves is doubtful and Sergio Busquets is suspended for Tuesdays game.I think were the team with the most goals scored so one thing offsets the other. If we can maintain this ratio we wont have to worry, coach Tito Vilanova said. Were trying to improve all aspects of our game to allow fewer goals. And Celtic is always a complicated opponent.Messis 15 goals including a league-high 11 are the main reason Barcelona is unbeaten through 10 games this season.Statistics are just a detail, the important thing is that we keep on winning, Messi said after his 59th goal of the calendar year.The Argentina forward has already scored 71 goals for club and country in 2012 to leave himself only four shy of matching Peles record of 75 in a single year in 1959.I dont know how you can stop him, said Celtic assistant coach Johan Mjallby, who watched Messis performance against Deportivo. He doesnt really play as a recognized striker. We know we cant switch off for a second. We know they are brilliant going forward.Messis goals have been aided by Cesc Fabregas, who stepped in to Xavi Hernandezs usual playmaking role with ease in guiding the attack at Deportivo. The former Arsenal captain has turned into a versatile player for Vilanova, who has used him in various positions throughout one of the best starts by any Barcelona coach to a season.Ive always had confidence in my abilities and Im working really hard, Fabregas said. Ive felt really comfortable in this system since the start of the season.Celtic is coming off its first Champions League away win in 21 matches but Barcelona is unbeaten at home in 17 in the competition. Celtic is winless in 12 trips to Spain although, the Scottish team has managed two draws at the Camp Nou in three visits.