The two teams will meet in the last 16 next month.
Speaking to ManUtd.com after Monday's Champions League draw, Valencia said: "If we can do our job and get a good result over there, then we always feel confident at Old Trafford.
"We'll take a lot of confidence from our performances in the Champions League so far this season. We qualified as group winners with a good points tally so confidence has been very high in the competition.
"It'll be tough but we're focused on trying to get through [to the quarter-finals]."