Christian Pulisic has been told what he needs to do in order to become one of the “best in the world”, with Chelsea boss Frank Lampard demanding even more from the United States international.A big-money arrival at Stamford Bridge from the summer of 2019 has enjoyed a productive debut campaign in English football. Several challenges have been overcome, including a slow start to life in the Premier League, an unfortunate injury at the turn of the year and the uncertainty caused by the coronavirus pandemic.Pulisic has cleared those hurdles in style, with the progress he has made in west London seeing inevitable comparisons drawn to former Blues star Eden Hazard.Lampard has been eager to avoid being dragged into that debate, with a 21-year-old attacker also keen to distance himself from links to a Belgian superstar who carried Chelsea for many years.Pulisic, along with those around him, are aware that he still has a long way to go before he can stand alongside iconic figures of the past and present.There is, however, confidence in the Blues camp that impressive development can be maintained, allowing a hot prospect to add even more qualities to his game and hit even greater heights.Lampard told reporters of his hopes for Pulisic ahead of an FA Cup semi-final clash with Manchester United on Sunday: “Well I have seen a real improvement in his all-round game.“Coming to the Premier League is very difficult because of the physical nature of the league and we have to remember how young he is and the summer he had.“I think he found those physical demands pretty strong in the beginning and now you are seeing him deal with it better. A lot of that can be credit to himself and how he has approached it.“He has worked a lot with our strength and conditioning coach, Adam Burrows, who is fantastic. They have worked a lot together, but it is Christian who has to take on that responsibility and he has. Physically that has helped him. “Also, just his talent is coming through. Looking forward, I probably want to see more of what he has shown in recent times, which is goals and assists, because that is what the best in the world do in that position.“I feel he has the capability to do that as he improves. That can be the edge as his game goes on and moves on levels.”Pulisic has taken in 31 appearances for Chelsea in the 2019-20 campaign, with nine goals and as many assists recorded across those outings.