Manchester United's results have turned around in recent weeks, with the club having won three of their last four Premier League matches and their last three games in all competitions. The Red Devils are in eighth place in the league and can continue their climb with a result against crosstown rivals Manchester City in the Manchester derby on Sunday, however a former United player isn't convinced by his old side's recent turnaround. More specifically, Dimitar Berbatov has raised concerns about how the team played in their midweek Champions League match. United claimed a 1-0 victory over visiting FC Copenhagen on Tuesday, but the match statistics were fairly even between the two sides and Harry Maguire's winning goal didn't come until the 72nd minute. "Let’s not be blinded by the three points and let’s not pretend we didn’t see some cracks in the team, Berbatov told Betfair. "Copenhagen were easily able to create goal scoring opportunities. They didn’t score due to [goalkepeer Andre] Onana and the inexperience of the Copenhagen players. That’s why it was 0-0 for most of the game. "This lack of communication, positioning, reading of the game, it needs to be addressed. Yes, it was 1-0 and three points, but I hope everybody will pay attention to the mistakes that were made in the game and correct them immediately. "Let me tell you something… If United allow the same freedom like they did against Copenhagen to City, they are going to suffer." Berbatov stressed that City will punish the kinds of mistakes he saw United make in their midweek clash. The former Red Devils' striker also implored his old team to ignore their rivals' recent dip in form, which saw the Sky Blues lose back-to-back league matches a few weeks back. "There are teams when you play against them, you can afford to make mistakes because you know if there’s a lack of quality in the opposition, they are not going to take advantage of the mistakes you’re making," Berbatov said. "But then there are teams when you know if you make half of a mistake they will punish you - teams like City. You need to be 100 per cent more concentrated against City. "Based on what City have achieved so far and how they’re still performing at a high level this season, I don’t think you can have the slightest thought of underestimating them in any way possible. "You need to get that thought out of your mind. Even if they are losing or not playing the way people expect to play, they still have so much quality in the team that the quality can compensate for a bad performance and get you the three points. "They are title challengers, they are Champions League challengers, they challenge for everything. The experience with their manager (Pep Guardiola) knowing when to play the right players during the season, and who rests when, it’s unbelievable and that is how you win trophies. This is what good managers do."