Lallana has not been in the starting line-up since the FA Cup win over Everton in early January after two setbacks from a thigh problem forced him to miss the first four months of the campaign.
Lallana has managed just 186 minutes of Premier League action since making his comeback from that pre-season injury in November, but against Porto he could be in line for his first European appearance since the 2016 Europa League final defeat to Sevilla.
“Adam absolutely was an integral part of the team… he is important to us,” said Klopp.
“But he needed only time. Life is to learn from your mistakes and we all have to learn.
“We made this mistake — he looked fit. Maybe two little setbacks, not the biggest setbacks, but in and out, in and out. So now we have to build with him. He is coming close.”
Klopp, whose team are locked in a battle with Manchester United to finish second in the Premier League, said 29-year-old Lallana lacked rhythm due to his time on the sidelines but he remained a key part of the Liverpool set-up.
Liverpool have one foot in the Champions League quarter-finals as they defend a 5-0 lead when they host Porto at Anfield.
Klopp will resist the urge to make sweeping changes even though only a remarkable comeback by the Portuguese club will stop his side coasting into the last eight.
That could mean the likes of 32-goal Mohamed Salah, who has played 3,060 minutes for his club this term, and 22-goal Roberto Firmino (3,053), will feature despite what is essentially a dead rubber.
“They are all desperate to play, to be honest,” said Klopp, who said he on the other hand was focusing on Porto instead of Saturday’s trip to Manchester United.
“When I said we will not rest any players I was thinking more that we will bring the best team we can have for this game.”
Salah has scored in nine of the past 10 matches and a goal on Tuesday would see him equal the club record of goals in eight consecutive matches set by Dick Forshaw (1924-25) and John Aldridge (1988-89).
He would be an obvious man to rest but Klopp said he did not know whether keeping the Egyptian playing is best for someone on such a scoring streak.
“These things are good for him. Both ways,” he said. “They are playing Saturday and Saturday and there is rhythm in that as well so we could say that is OK — do we need a Tuesday game for the rhythm?
“I’m not sure. I don’t think there is a 100 percent answer.”