United were reliant on Swedish striker Zlatan Ibrahimovic, who scored 17 league goals - and 28 all told - before a cruciate knee ligament cut short his season in April. Then, when you're in the Champions League last 16 draw, anything can happen.
"It's the objective of every one of the top teams and every one of the top team managers". After a first season of transition, Mourinho must stamp his authority on this team and is under a lot of pressure to deliver the coveted Premier League title.
Mourinho says he is after another player "coming from the sides" to complete his summer business - leaving the door open for either a winger or a full-back.
"It's not something urgent, that we are desperate to have it done or not done, I just think that he was very clear by showing what he did past year was not enough for him".
"He had a good fight against two good central defender and I am happy with this period and how he fits into - I am never exhausted to repeat - an awesome group".More news: North Korea tensions continue to weigh on global stocks
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And Mourinho admits that the Red Devils will have to deal with the weight of history on their shoulders when they return to the competition proper.
"In the last two or three seasons they've been defensively okay but not scoring enough goals has hurt United and I think there are goals in the side now". We'll take it step by step and be humble.
However, Mourinho has lost a number of key players to long-term injury, including defenders Marcos Rojo and Luke Shaw, and wing-back Ashley Young.
Hammers boss Slaven Bilic said: "It's not ideal playing there first game of the season, but on the other hand, it is brilliant and one of the greatest away games in the league".
"I understand the reality of the market, of the numbers and that my club by doing 75 percent of what I initially asked did very well". If we manage that, we'll try to finish in the top two.