Keita was taken off midway through the first half of Liverpool's 3-0 loss to Barcelona in the first leg of their Uefa Champions League semi-final clash at Camp Nou.
The midfielder sustained a knock after being hauled down by Ivan Rakitic. However, he continued to play before he eventually had to be taken off.
"It was really unlucky. Bad news. High-grade adductor injury. The tendon is ruptured. Will keep him out for at least 2 months,” Klopp told the media in Europe.
“Bad news for us and for Guinea with the Africa Cup of Nations coming up. Not nice.”
The news comes as a huge blow to Afcon-bound Guinea. Injuries and inconsistency had stunted the growth of the midfielder at the Anfield outfit, having arrived in the summer as a £59 million ($62m) signing.
Guinea are in Group B of the Afcon 2019 alongside Madagascar, Nigeria and Burundi.
They will most likely hang on to the slim hope that their midfielder might return to action later in the competition.
Asked about how Keita is taking the news of his recent injury on board, Klopp added: "For sure he’s not in the best moment but it’s okay I think.
“There are two things: a very interesting part of the season he’s not part of, on the other hand, Guinea I don’t think is a regular [qualifier] for the Africa Cup of Nations. That was, for sure, a big target for him as well so he is not in a good moment.
"That’s a moment when you have to help the players, we try everything we can."