Midfielder Fabinho, who has been deputising at centre-back, limped off against FC Midtjylland with a hamstring injury and with Virgil van Dijk out for a number of months with an ACL injury, Liverpool's defensive options were dwindling.
However, Klopp confirmed that Matip trained fully on Sunday while midfielder Naby Keita is also close to being fully fit.
"Naby and Joel trained yesterday fully," Klopp said at a news conference on Monday. "I haven't made any decisions yet. We are still two days after the game. We have to wait until medical department gives us green or orange or red light.
"We have at the moment more centre-halves available than we probably will line up together, which is good."
Liverpool head into Tuesday's game fresh off their 2-1 win over West Ham on Saturday.
Mohamed Salah came in for some criticism for his role in the build up to their first-half penalty, with ex-Aston Villa and Chelsea forward Tony Cascarino accusing him of diving, but Klopp gave those suggestions short shrift.
"No. I don't know what people think. It was a foul, anybody who saw the situation saw it," he said. "I spoke to Mo yesterday morning about how he feels and he has exactly three proper knocks on the foot and one of them is from the penalty situation. That's how it is.
"We don't talk that long about penalties we don't get in other games but there was clear contact so no, I don't understand the criticism."
Liverpool are in Bergamo ahead of their match against Atalanta on Tuesday and Klopp has said it will be the "biggest challenge" his side have faced in the Champions League so far this season.
He praised the Italian club's recruitment policy and said Atalanta "play to their system with 100% conviction," likening their style to how Leeds United play under Marcelo Bielsa.