Coutinho was ineligible to play for Barcelona in the Champions League, having starred for Klopp's Reds in the group stages of this season's competition before moving to the Nou Camp in January.
Against all odds, Liverpool have ended up going further than the competition than Barcelona, who threw away a three-goal lead to lose to Roma on away goals.
“Hopefully Phil does not have regrets because we wish him all the best," said Klopp, as quoted by the Mirror. “I never said that we would be stronger without him because he is a world-class player with a world-class future.
“I would love to have him around at this moment, but we had to decide. When it became clear that we could sell him in the window then we had to do the deal and find other solutions.
“I just thank God that the rest of the boys have worked really well together."
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Liverpool have thrived in Coutinho's absence, with Mo Salah, Sadio Mane and Roberto Firmino thriving since the Brazilian left the club. The forward trio have 83 goals between them this season.
“We had no idea that they would score so many goals," Klopp said of his fab three. "Of course, we thought they would all work well together, but not like this.”
Coutinho left Anfield to win trophies and he got his first since joining Barcelona on Saturday, scoring in a 5-0 win over Sevilla in the Copa del Rey final.
Liverpool are competing to reach their first Champions League final since losing to AC Milan in 2007.