The two teams will meet in the Champions League on Wednesday, having both already qualified for the knockout rounds.
"It's a huge and exciting challenge against a team who could win the Champions League," the former Spain coach told reporters.
"They are the best attacking team in England at the moment, they have great players.
"It's a real excitement to play against them and it motivates us to play our best."
On dealing with picking his team amid the coronavirus pandemic, Lopetegui added: "We want to keep working and growing as a team against a very strong opponent who we'll need to be at our absolute best to beat.
"I see the team working every day, they're trying their best in spite of the difficult of this season and the injuries we have. We've got a number of absentees but we are coping."