Javier Hernández will return to Old Trafford as a West Ham player on Sunday and says he feels “only happiness” towards the club that brought him to the Premier League seven years ago. The Mexico forward expects to make his competitive debut for Slaven Bilic’s side at the stadium he called home for four seasons; the venue brings positive memories although he admits to being “shocked” when Sir Alex Ferguson, who signed him from Guadalajara, retired in 2013.

“I can just say it’s luck,” Hernández said of the fact his return to English football, having spent two seasons at Bayer Leverkusen before joining West Ham for £16m last month, comes against United. “It was a great experience [there] … only happiness. I was living my dream and made that big step, which is not common.

“There is nothing negative about going there. It’s going to be my first game with my new club, against my old club in my old house. It’s only positive things – it’s an important moment for me.”

Hernández scored 59 goals in 157 appearances for United during a five-year spell that also brought a season on loan at Real Madrid. He helped them win Premier League titles in 2010-11 and 2012-13 under Ferguson, averaging almost a goal every two league games in each of those campaigns, and says he was jolted by the sudden departure of the long-serving manager.

When asked if Ferguson’s announcement was a surprise, he said: “I didn’t see it coming. Nobody did. It was very strange. We were shocked but we were very respectful too because he decided squads, games, everything … it was his life.

“He was the manager who brought me here and opened the door to Europe. He taught me to be a better footballer; we won the 19th and 20th Premier Leagues for Manchester United together, so of course I was going to be upset when I had a good relationship with a person who gives you a lot of confidence and helps you to improve as a person and a player.”

Hernández’s form at United tailed off after Ferguson departed. He scored nine times in 33 appearances the following season but would make only five more appearances thereafter, eventually furthering his career in Spain and – with considerable success – Germany. He accepts United’s wider fortunes dipped to a greater extent than he had expected.

“Everything changed [when Ferguson left],” he said. “I cannot only tell you one thing. I don’t say this in a good or bad way, it was just change, and we didn’t respond as well as David Moyes or we wanted to. Nobody wants to be out of European competitions or not fight for the title.”

Hernández during his press conference on Wednesday. Photograph: Arfa Griffiths/West Ham United via Getty Images

Both of those goals appear a long shot for a West Ham side who finished 11th in last season’s Premier League. Hernández is viewed as the cure for a malaise that has seen a string of often underwhelming centre-forwards shuttle through the club over recent years but says he bears no extra burden.

“I feel the same as when I went to Manchester United, when I went to Real Madrid and Leverkusen, and now West Ham,” he said. “I am going to play football, which is something I was fighting for since I was a kid, and then we will see what happens. It’s easy to say I can score 20 goals, or that I have a lot of pressure, or not, or blah, blah, blah. Speaking is very easy but the most important thing is to prove myself on the pitch.”

Hernández felt flattered to hear José Mourinho say he could have scored “20 goals easy” at United last season but pointed out, with no sense of bitterness, he “didn’t get the chance to prove it”. He prefers to focus on the sense of possibility in reviving his new club and believes he can fulfil his ambitions there.

“I’m looking at it as a challenge in the same way as when I go with the national team or any of the clubs I played for before,” he said. “It’s football, I want to keep doing it and show I can achieve the things I dream of, and I think I can.”