Manchester United manager Sir Alex Ferguson has warned injured striker Wayne Rooney that he faces a fight to displace in-form Javier Hernandez.The Mexican international has made an immediate impact at Old Trafford this season and has now scored two goals in as many games after opening the scoring for the Red Devils in the 2-1 victory over Stoke on Tuesday night.Nani also scored on his return to the United starting line-up and after the game Ferguson revealed it was going to be hard to leave out 'Chicharito'.“Of course it will be hard to leave Chico out - that's the kind of problem you want,” Ferguson said, according to The Sun."Over the years the strikers I've had have always given me that problem."If Chico keeps sticking the ball in the net it does give me a problem."The striker has now scored nine goals for United this season – compared to Rooney’s three - and the England international’s ankle injury will keep him out of the FA Cup clash against Liverpool at the weekend.And Ferguson believes that the new year can only mean his players can only get better.He continued: "Once you get to new year and you're in there it gives a good guide to where you're going to be at the end of the season."Our history tells us we play better in the second half of the season and we relish the big games."We're pleased with where we are. We're going to be in the shake-up."United are still unbeaten in the league after 20 games, yet many critics are suggesting that they are not playing well."We're always having to respond to that," said Ferguson. "You can look at as many stats as you like."But look at our home record for a start. Some of our performances have been fantastic."We're an easy target for that kind of thing. We just have to dismiss it and concentrate on our ambitions - and that's to win the league."Source: Goal.com