The Swedish striker was released by United at the end of last season after he suffered a serious knee injury back in April in the Europa League quarter final tie against Anderlecht.
West Ham manager Slaven Bilic has reshaped his squad extensively since last season's 11th-place finish. Anthony Martial and Henrikh Mkhitaryan claimed four apiece and Jesse Lingard scored once in the league.
"I don't think we're going to see that replicated (in England)", said Premier League chairman Richard Scudamore.
Ibrahimovic, who has won 33 trophies in a highly-successful career, believes he still has one or two more years left in him despite his age - and can offer a lot to United, with young players like Marcus Rashford, Lukaku and Anthony Martial all looking to learn from his experience.
Mourinho reiterated at a pre-match conference yesterday his satisfaction with the club's transfer business this summer window, despite not achieving "100 per cent" of his targets. "I don't think I am in a position of moaning, crying, contesting or to say I am not happy with it", the Portugese continued.
"We are in a position to do quality work better than we did in the first season, so I am convinced - it is not just a hope, I am convinced - that our second season, in terms of the quality of our team, is going to be better".
Mourinho knows they were over-reliant on the injured ex-Swedish striker's goals and wants more support for this season's main man Romelu Lukaku.
"I'm here to score goals and be the focal point of the team", Lukaku said.
Despite that miss potentially denying United a chance at taking the Champions League winners the distance, Mournho was happy with his new No.9.
"That is why the club was clever to do that because we anticipated what we needed and we tried to do our best, not just for next season but the future". Paul Clement's Swansea are another team that secured plenty of profit for their fans from their 12 league wins, beating Liverpool, Southampton and Everton as they managed to avoid the drop.
He said: "It's not because I have always done it that I am going to do it".
"Their summer signings have improved the team and I don't think Pep Guardiola has stopped spending yet".