Lopetegui felt they had enough chances to nick the three points from the French champions on Wednesday evening.
He later said: "We played a very good game in the first half, we had a lot of situations where we could have scored.
"They had one when we lost a ball and I don't remember another in the whole match. We defended very well against a very dangerous team with a lot of talent up front. I thought we had enough chances but we lacked precision in the penalty area.
"We played as a team and managed to minimise their talents. We had a lot of options [to score] but perhaps we lacked a bit of calm.
"In the end we didn't score and when you don't score against a team with so much talent you can lose. This is the Champions League and a team who won the league in France."
On their injury record, Lopetegui added: "We have problems. It's what happens in a difficult period with national-team games, and the accumulation of matches and travel.
"We lost Karim [Rekik] and Marcos [Acuña] had problems. [Koundé] has not recovered from the injury he suffered playing for France against Spain."
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