Villas-Boas this summer became the seventh manager charged by billionaire owner Roman Abramovich with delivering European glory and will begin his first attempt to do so on Tuesday when the Blues kick off their Group E campaign against Bayer Leverkusen. Chelsea have gone closer than anyone to winning the Champions League without actually lifting the trophy since Abramovich bought the club eight years ago. But after reaching four semi-finals and one final in the Russian's first six years at the helm, they appeared to go backwards in Europe under Carlo Ancelotti, failing to get to the last four in 2010 and 2011. As well as sparking increasing criticism of the age of the squad, it also led some to question whether there was now a mental block preventing Chelsea's players from taking that final step. But Villas-Boas, who will be making his managerial debut in the competition on Tuesday, said: "I don't think there's a mental block. There's some kind of unpredictability that can take you all the way to the final sometimes. Other times it doesn't." The 33-year-old, who worked as a scout under Jose Mourinho when Chelsea lost two semi-finals to Liverpool, added: "It always depends on the draw that you get. "This club has been present in semi-finals. "We came close in the first one against Liverpool (in 2005). Then they made it to the final, where they merited it. "They were close again when Barcelona reached that first final for Pep Guardiola's team (in 2009). "We've been close to getting it. We'll just try to be close again this season to go all the way." With Abramovich having unceremoniously dismissed almost every other manager who failed in that quest, it seems certain Villas-Boas will have to deliver the Champions League if he is to remain in charge longer than his three-year contract. But he said: "It will become never-ending if we address it like this. "I don't think I'll be judged on it." With Barcelona having swept all before them last season and looking potentially even stronger this term, it would be unfair to judge Villas-Boas should he fall short in his debut season. "It's not just Chelsea as a top European club who haven't won it," said the Portuguese on Monday, who described the Champions League as "the most difficult competition" around. "Our time will eventually come. We just have to focus on making it one of our objectives, as it has been for the past few seasons." What is unlikely to be tolerated is Chelsea failing to get out of a group that also contains Valencia and Genk. Villas-Boas offered the usual respectful platitudes to the Blues' Group E rivals on Monday. But his true assessment of the threat of Leverkusen will be revealed by his team selection, especially with Sunday's Premier League trip to Manchester United on the horizon. "You'll see some changes tomorrow. Then we'll make wise decisions for Sunday," said Villas-Boas, whose big decision once again revolves around whether or not to select Fernando Torres. Daniel Sturridge certainly did enough to start alongside or instead of the misfiring Spaniard in Saturday's Premier League win at Sunderland, although Villas-Boas was reluctant to lavish praise on the 22-year-old. He said: "He had a three-game ban and has just returned, and he had motivation to have an impact in that game. It was the team, also, who made him perform to that level."