United and Sevilla will go head-to-head in Cologne on Sunday for a place in the final on Aug. 21.
It will be the first meeting since Sevilla dumped United out of the Champions League in 2018 -- a result which prompted Jose Mourinho to claim the Spanish side had a bigger "football heritage."
"We are going to play against Manchester United in the next match," Lopetegui, who led his team to a 1-0 win over Wolves in their quarterfinal in Duisburg on Tuesday, said.
"They're the biggest team in the world but we're going to be prepared for them."
"It's something we're really looking forward to, both as players and fans," Bounou said.
"The Europa League is an important competition for the club and we go into the tie up for the cup, focused on the next game and nothing else.
"I've been practicing saving penalties. I know Raul from our time together at Atletico Madrid so I knew a little bit how he tends to take them. But you always need luck, too."