"It's another muscle - it looks like, hopefully, only a little tear", the manager told liverpoolfc.com at a post-match press conference.
Speaking to reporters after the game, Klopp offered his insight into where Keïta might play next season and his thoughts on Daniel Sturridge's impressive form.
"Of course that's not ideal for me, but I can not say much more about that either", the 25-year-old said.
Set-pieces were probably the most positive thing today. But for that to happen we need a strong squad around him and Loris is an outstanding goalkeeper.
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This made for uncomfortable viewing as Liverpool fans bemoaned the German.
Later, the 19-year-old followed up with a spectacular goal in the 89th minute to put Dortmund one goal ahead.
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We're feeling the Monday blues today as the 2018 World Cup has come to an end. (We have) different origins but we are all united. We waiting for the final knockout that finally arrived over Pogba and the match was resolved. "The World Cup... it's a lot...
Netherlands' Virgil van Dijk opened the scoring for Liverpool in the 25th minute with a perfectly timed leaping header off a long cross from Andrew Robertson.
Jurgen Klopp doesn't know if Christian Pulisic will ever join him at Liverpool, but he thinks Dortmund is a good place for the American to develop.
However all did not go to plan, with the United States global unable to be given the prize as it was a large alcoholic beverage sponsored by beer brand Heineken.
But the collapse can only have added to any doubts embattled keeper Loris Karius may have had about the future, especially in light of Liverpool's world record purchase of Roma stopper Alisson last week.
USA president arrives in Helsinki to meet Russian leader
Trump and Putin will meet today (16 July) in Helsinki for their first stand-alone meeting since Trump took office in January 2017. For Trump , the formal meeting with Putin is an opportunity to develop a closer working relationship with the Russian president.
Liverpool will fly to NY on Tuesday morning ahead of their second International Champions Cup game, when they will face Manchester City the following day.