Manchester United manager Sir Alex Ferguson admits he is apprehensive ahead of the Champions League semi-final first leg against Schalke 04. United have never beaten German opposition in a two-legged European tie during Ferguson's long reign. And the Scot insists he is not taking surprise package Schalke lightly, saying: "Semi-finals are never easy. "This is going to be a difficult game and we will treat it that way," he said ahead of Tuesday's match. Schalke are currently 10th in the 18-team Bundesliga but stunned reigning European champions Inter Milan in the quarter-finals, beating them 5-2 in Italy and 2-1 at home to set up their tie with Ferguson's men. "Schalke have beaten every team at home in the Champions League this season, including Valencia and Inter Milan. If you just take that in isolation, it is good form. United will compete in their 12th semi-final when they meet Schalke in the Veltins-Arena, but only four of those resulted in an appearance in the final. Last season they were knocked out by Bayern Munich at the quarter-final stage, and there were defeats to Borussia Dortmund and Bayer Leverkusen in the last four in 1997 and 2002 respectively. Ferguson was successful against German opposition in the stunning 2-1 win over Bayern Munich in the 1999 final in Barcelona, but says that when you reach the last four, expectations are even greater. "You always get apprehensive at this stage of the competition. We had the same situation in 1999 when we played our semi-final against Juventus," he said. "There was an apprehension in our first game at home that we released in the second leg. When we played Barcelona in the first leg [in 2008] we got the result we wanted. But the last 20 minutes of the second leg were absolute agony." "There is no way we will be led into believing this is going to be easy," he added. Ferguson admitted United's failure to turn more of their semi-finals into finals and European titles was a thorn in his side. "This is where we should be. The expectation has always been high with regard to the European scene and you do get envious of other clubs' great record in Europe. "You look at Real Madrid (nine wins and three runners-up spots), AC Milan (7-4), Bayern Munich (4-4), Ajax (4-2) and Liverpool (5-2). We are trying to gain parity with that. "We really need to progress quickly to get to that level, and the present group have enough experience in Europe now." Schalke manager Ralf Rangnick, who only took charge at the club in March, said the pressure is all on United. "Of the two teams, we have much less to lose. We may be less experienced, but we are hungry and we have a lot of passion. "Against Inter, we compensated for our lack of experience with our enthusiasm, our commitment and our discipline. It's up to us to reproduce that in front of our fans and at Old Trafford. "It's an important match for all of us. Who knows how many players in this team will find themselves in this position again?" He added: "United are a very organised team. I expect a close game and a result that may give us a chance in the second leg." Meanwhile, United goalkeeper Edwin van der Sar has pinpointed Schalke's veteran Spanish striker Raul as the main threat to his team's hopes. "Raul is quite an amazing player," said the Dutchman, who will be appearing in a record-equalling 13th Champions League semi-final. "He had so many years at Real Madrid at a high level and scored so many goals for them in the league. In addition, he is top scorer in the Champions League [with 71 goals]. "He is not someone you can lose sight of - he is so dangerous and only needs a little chance to score. Our defenders should be on their toes." Van der Sar, 40, who retires at the end of the season, added that facing either Real Madrid or Barcelona in the final at Wembley on 28 May would be a fitting finale to his playing days. "I have had a reasonable career so far. Let's hope I can finish it off nicely." Source: BBC