Keita limped off as Barcelona defeated his side Liverpool on Wednesday in the first leg of their UEFA Champions League semi-final clash at the Camp Nou.
"Bad news, a high-grade adductor injury with the tendon rupture so it keeps him out for at least two months," said Klopp of Keita, who will now miss Saturday's trip to Newcastle, as well as home games against Barcelona and Wolves -- Liverpool's last match of the Premier League season.
"Bad news for us and for Guinea with the Africa Cup of Nations coming up. Not nice," German boss Klopp added.
"Very serious. For sure he is not in the best moment. African Cup of Nations was a big target for him."
Manchester United's Eric Bailly was ruled out of the Africa Cup of Nations after the Ivory Coast defender suffered a knee injury against Chelsea, the Red Devils announced on Monday.
Bailly sustained medial ligament damage in a collision with Chelsea midfielder Mateo Kovacic in the second half of Sunday's 1-1 draw at Old Trafford.
The 25-year-old was making his first Premier League start since February 3 but now he will be sidelined for the Africa Cup of Nations, which starts on June 21 in Egypt.
The 2019 Africa Cup of Nations will be staged in June 2019 in Egypt.