Hernandez not surprised by Manchester United's struggles since Ferguson retired

The 29-year-old joined West Ham 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 Hammers debut at Old Trafford on Sunday.

Hernandez won two Premier League titles during his time at United, the second of which came in 2013 as Sir Alex Ferguson retired in style by delivering another trophy for the club.

Since Ferguson left his post, United have had four managers; David Moyes, Ryan Giggs, Louis van Gaal and now Jose Mourinho.

But that success of 2013 remains the last time the Red Devils won the league and they have finished outside the top four in three of the past four seasons.

That does not come as a surprise to Hernandez, however, as the Mexico international always felt Ferguson's departure would have a knock-on effect.

"The change of Sir Alex retiring, we knew it was going to be very difficult. He was unique in (the) history of football," he said.

"We all knew there was going to be a transition. You cannot have a manager for 26 years - the best manager in history, achieving everything, changing the squad every couple of years, changing players, even all the staff sometimes, there was always going to be a transition.

"I wasn't surprised. It was normal. Nobody expected when we played for David Moyes that we wouldn't be in European football. But that is part of football."

Hernandez hit 59 goals for United having been signed as a relative unknown from home-town club Guadalajara in 2010.

And he concedes Ferguson gave him plenty of life lessons that he has carried with him ever since.

"He told me a lot. He was a manager who liked to stay in contact with his players," he said.

"The one piece of advice I remember when I came was to keep going and doing what I was doing in the national team for the club and to keep that confidence.

"He liked me and that is why he brought me to Manchester United.

"I didn't see it (his retirement) 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, 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 a lot to improve as a person and player.

"He gave me a lot of opportunities to live this dream. Of course you are going to be upset when he says he is not going to be around working with you any more."

Hernandez is now set to return to Manchester with his new side and admits it will be an emotional time - and that he has a decision to make over whether to celebrate if he hits a debut goal for West Ham.

"It's going to be emotional, of course, to be in my old house against my old club," he added.

"With my new team, my new chapter. I want to do as best as I can. It's an important moment for me. I don't know if I will celebrate if I score at Old Trafford.

"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."