Dalot has played twice for the under-23s since recovering from knee surgery and completed 90 minutes for Ricky Sbragia's side in the 1-1 draw with Reading at Old Trafford on Friday.
"We decided not to bring Valencia because his knee is not a knee that needs an artificial pitch at all", Mourinho told reporters in the Swiss capital on Tuesday.
With a reference to Switzerland's greatest sportsman, 20-times Grand Slam victor Roger Federer, Mourinho urged his team to just get on with it.
United may have been European champions three times, but they come into this season's continental campaign determined to make amends for a feeble exit from last season's Champions League, when they were beaten by Sevilla in the last 16.
"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 on such a surface but he has to play and he has to win".
Mourinho does not need to be reminded of the potential pitfalls of a visit to Switzerland, however.
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Jose Mourinho has not been happy with the club's transfer business this summer and was not allowed to have a winger or central defender in his squad for the season as requested. Basel also dumped Alex Ferguson's United out in the group stage back in 2011-12.
Despite being suspended for Saturday's Premier League win at Watford, Rashford was the subject of a long Mourinho rant ahead of the game, with United's manager taking aim at media pundits who have criticised his use of the talented attacker.
"So I think he's in the flawless spot and he's getting enough games to continue his development".
The Manchester United manager has left Antonio Valencia at home for tonight's match against Young Boys because he is anxious that the club's captain could suffer a serious knee injury.
The two-time Champions League victor believes football has evolved beyond the days of players being pigeon-holed in one position and Rashford's versatility is an added string to his bow.
"We need to protect his clinical situation", Mourinho said.
"They have the quality, speed and technique to play on this pitch".