Sir Alex Ferguson sought to dampen down some of the excitement surrounding his Manchester United team on Tuesday, as they prepared to open their Champions League campaign against Benfica. United tackle the Portuguese giants in their Group C opener at the iconic Estadio da Luz on Wednesday, having begun the defence of their Premier League title in scintillating fashion. Four straight wins have put them top of the table and their haul of 18 goals is the highest tally after four English top-flight games since Wolverhampton Wanderers plundered 20 in as many matches in 1947. Expectations have soared following the 8-2 annihilation of title rivals Arsenal last month and Saturday's 5-0 thrashing of Bolton Wanderers, but Ferguson believes it is too early to assess his team's worth. "We've only played four games," he said at his pre-match press conference on Tuesday. "The quality of our play has been superb, but it's a young squad. "Obviously there'll be a time when their form tapers off, so I hope the experienced players will then step in and add to the great start to the season we have had. "You can't judge a team after four games. But hopefully they'll become one our best teams." Ferguson confirmed that centre-back Rio Ferdinand had been left behind in Manchester as a "precaution" ahead of Sunday's visit of Chelsea in the Premier League. The Scot also revealed that captain Nemanja Vidic was around "two weeks" away from making a comeback after his calf injury, but said he had faith in his squad's ability to compete on several fronts. "The season really starts when the Champions League comes around," said Ferguson. "You have games on Saturday, Wednesday, Saturday, Wednesday all the time. "We're coming to a period where we have a game tomorrow (Wednesday) and then Chelsea on Sunday, then Leeds (in the League Cup) on the Tuesday and then Stoke away on the Saturday. The squad will obviously be used." With Ferdinand and Vidic out, Ferguson will hope that Jonny Evans is able to line up alongside Phil Jones at centre-back despite having sustained a hip injury in the game at Bolton. Ferguson had suggested that he could turn to the more experienced players in his squad for Wednesday's game, prompting speculation that Dimitar Berbatov could be recalled, but he hinted he may yet keep faith with the players responsible for his side's storming start to the campaign. "I haven't decided for tomorrow (Wednesday) yet, but it wouldn't worry me at all to play the team that's been doing well," he said. Ferguson's side have not lost an away game in 18 months in the Champions League and finished last season's tournament without conceding a single goal on the road. Despite a six-game winning streak at home in Europe, Benfica coach Jorge Jesus conceded that United's dominance meant his side were likely to face a scrap for second place in the group with FC Basel and Romanians Otelul Galati. "It's going to be a very close fight for all the teams in this group," he said. "Manchester United are clearly the favourites but it will be a fight to the end between the other three teams. Jesus added: "Manchester United have been very strong over the last two years. We've only won once in seven matches against them in the Champions League, under Ronald Koeman (in December 2005). "If we win we'll be very, very proud of that achievement." Jesus confirmed that experienced playmaker Pablo Aimar would play on Wednesday after starting on the bench in Saturday's 2-1 defeat of Vitor Guimaraes, but insisted that United's injuries would not weaken them. "They've been playing with young players in defence and they're worthy substitutes," he said. "It won't change the way we play."