Michael Ballack believes Frank Lampard and Steven Gerrard can forge a formidable midfield partnership, but only if they "pull their egos back".[LNB] Questions have been raised in the past about whether Gerrard and Lampard can link up effectively at international level but they are expected to play together in England's World Cup opener against USA on Saturday.[LNB]Ballack admits they are two similar players who prefer to get forward rather than provide a defensive shield and he is aware of the problems that have previously been encountered.[LNB]The German has now told the pair they will have to make "sacrifices" and not worry so much about scoring themselves, but he is convinced they can combine successfully.[LNB]"Gerrard and Lampard should be intelligent enough to make it work," Ballack, a team-mate of Lampard for four years before being released by Chelsea this week, told The Times.[LNB]"They've had problems before, but have to pull their egos back for the good of the team. [LNB]"They can't just play as they do for their clubs as they both want to get forward and are a little bit similar. If they pull back a little bit, they can make it work easily. [LNB]"If you play for a big team you are surrounded by good players, so you can't just think 'me, me, me!' all the time. [LNB]"You have to make sacrifices. It would be a shame if they weren't smart enough to work it out. I would love to have one of them in the German team, never mind two." [LNB]Ballack has been ruled out of the World Cup through injury and will have to follow Germany's progress from afar.[LNB]He is also interested in seeing how England perform and feels they could be lacking in mental strength when it comes to the big moments.[LNB]"They've lost a lot of tight matches, particularly on penalties, and this can play on your mind," he said.