West Ham striker Javier Hernandez admits he does not know if he will celebrate a debut goal against former club Manchester United. The 29-year-old joined the Hammers from Bayer Leverkusen this summer, two years after he left United for the Bundesliga side.The luck of the Premier League fixture list means he is set to make his West Ham bow at Old Trafford on Sunday.Hernandez, who scored 59 goals in his time in Manchester, will have a decision to make if he manages to open his West Ham account."I don't know if I will celebrate if I score at Old Trafford," he said."It's my old club, my old fans, my old stadium but it'll be my first goal for West Ham."I am not thinking about the celebration, I just want to have the chance to start and get my team the result."I am very happy and glad, it's the best way to come back and open at Old Trafford."I am a Hammer, a West Ham player, I want to do even better than I did in Manchester."Hernandez found his first-team options limited during his final days at United and even spent a season on loan at Real Madrid in an attempt to play more football.He left for Leverkusen in 2015 - with current United boss Jose Mourinho since insisting he would never have allowed the Mexico international to leave had he been in charge - but Hernandez says he does not rue his decision."I never have regretted leaving Manchester United," he said."I had some great experiences there and it helped me when I did move on."Hernandez is one of a number of new arrivals at the London Stadium as Slaven Bilic looks to build a squad capable of improving on the 11th-placed finish last season.Manchester City goalkeeper Joe Hart has joined on a season-long loan while his former team-mate at the Etihad Stadium, Pablo Zabaleta, has also come in.The club broke their transfer record to bring in Stoke's Marko Arnautovic with midfielder Sead Haksabanovic signing from Halmstad earlier this week.Hernandez is a big fan of Hart and believes the new crop can help West Ham qualify for continental competition."The European spots are the main goal for us this season. No doubt," he added."Joe Hart is a great lad, a great professional. He always gives 100 per cent on the training ground."He has been in the national team for so long, playing in the Champions League, he is a great goalkeeper."