Marcus Rashford has “a big opportunity” to become Manchester United’s main striker this season, according to Jose Mourinho – but he has to score more goals.United began the post-Romelu Lukaku era in some style, thrashing Chelsea 4-0 at Old Trafford with two goals from Rashford to ease concerns that they don’t have enough quality in attack.Mourinho thinks that Chelsea’s tactical naivety meant the game was well set up for Rashford to thrive, but that he can improve as a player with the added weight of responsibility this year. Article continues below Editors’ Picks Emery out of jail – for now – as brilliant Pepe papers over Arsenal’s cracks What is Manchester United’s ownership situation and how would Kevin Glazer’s sale of shares affect the club? Ox-rated! Dream night in Genk for Liverpool ace after injury nightmare Messi a man for all Champions League seasons – but will this really be Barcelona’s? “He has to score more goals,” Mourinho said on Sky Sports.“Especially without Lukaku in the team it will probably be these two [Rashford and Anthony Martial], plus Alexis [Sanchez] and Mason [Greenwood]. He will be on the pitch all the time and he has the qualities to be better and better and better.“He has the ambition and work ethic, he wants to improve, he wants to work. This season he has a big opportunity to be a better player and score more goals.“It depends on the way they play. Playing the way they played today against a Chelsea team that allowed them to play the way they like to play, he is very dangerous. Against teams with compact blocks, a lower block, that are more physical, I think it is a bit more difficult for them.”Mourinho was keen to point out that, while United were good value for their win and would be right to feel pleased with their performance, not every team will be quite as accommodating as Chelsea were.Frank Lampard was looking for a statement performance in his first game in the dugout, but his side struggled to pick United’s defence apart and couldn’t contain them on the counter.“People have to respect them,” Mourinho added. “This is not the Manchester United of ten, 15, 20 years ago but it is Manchester United. There are some very good players.“You have to know the qualities you have and the weaknesses that you have, and you have to know the qualities and the weaknesses that the opposition have.“For example, Chelsea today, they stuck to a plan where they were thinking more about their own identity and less about United’s identity and their strengths.“When you have Marcus Rashford playing there on the left, you have to think about that because he can hurt you.” Check out Goal’s Premier League 2019-20 fantasy football podcast for game tips, debate and rivalries.