The Reds return to continental action on Wednesday evening in Bern, where group stage debutants Young Boys could have an advantage thanks to the Stade de Suisse surface.
"I don't want to use (the artificial pitch).as a possible excuse for a poor performance", the Portuguese told a news conference.
"They have the quality, speed and technique to play on this pitch". Everyone knows its different but I had to say, I said last week in Geneva UEFA meetings we had, what can I say.
"I can get as an example, we are in Switzerland, the home of one of the best ever tennis players, and I'm pretty sure that the big man sometimes is not happy to play in such a surface but he as to play and he has to win. Apart from that, we go with everything we can, and we have to try to win".
"Valencia is the only one that we need to protect, his clinical situation".
"We'll try to play our football, we know it's going to be a tough game but we need to play our best football to win".
David De Gea is likely to start on Wednesday night and the Spaniard is hoping to end a disappointing run in the Champions League that has seen United reach just one quarterfinal in the last seven years.
"Rashford will learn about other positions when he plays in them which is good for his development but long term I think he'll be a number nine like Thierry Henry".
"I think it's very premature to talk about our chances when we have not played the first match". "Of course he has".
Mourinho explained that he is concerned over the potential impact of Young Boys' artificial pitch on the United captain's knee, with Dalot, Ashley Young and Matteo Darmian the options.
Having served the first of his three match domestic suspension in the win over Watford on Saturday, Rashford is expected to come back into the United line-up for the Champions League opener.
The 20-year-old was handed the number 10 shirt in the summer but Rashford has struggled to dislodge Romelu Lukaku and Alexis Sanchez.
"We have Lukaku, Rashford, Mata, Alexis, Martial - they all can not play together, so try to be a little bit happy for the ones that are playing and not be critical of the ones that are not".
"We're not used to playing on artificial grass so it's going to be a bit different - probably more hard for us".