Dec 11 (Reuters) - Manchester United ( MANU ) manager Ruben Amorim said the departure of sporting director Dan Ashworth was a difficult situation for the club but that nothing had changed in terms of their aims.

Ashworth left the Premier League club on Sunday by mutual agreement after only five months in the job.

"Of course, it is a bad situation like I said because you are talking about a human being, a professional that supports us as a team," Amorim told reporters on Wednesday.

"The most important thing is that the vision is really clear and that vision does not change only because one person leaves."

Amorim described Thursday's Europa League clash at Viktoria Plzen as a must-win game for his team.

United sit 12th in the Europa League table with nine points, comfortably in the playoff section, but need a win in the Czech Republic to stay within reach of the top tier.

"It is really important for us as a club, as a team, in this moment that if you pass to the next stage without playoff, you take two games from our schedule and that is massive," Amorim said.

"We have to be so much better in set-pieces and we have to win it. It is so important that we win but not just win but to play well."

When asked about possible transfers in January, Amorim said that developing players was the priority.

"We have to arrange a lot of things in our club before just buying and selling players. Let's focus on improving our players, improving our academy and then we will see," he said.

"Like any other team when the window is open we can do something but in this moment, our focus is to win games and we have to have this feeling of winning, and we have to start tomorrow."