Lallana went into the international break with a groin injury suffered during Liverpool’s last outing away to Swansea City, while Wijnaldum limped off during the Netherlands’ 1-0 defeat to France on Monday.
The October break handed Klopp a number of potential issues as he prepares to welcome United to Anfield.
But speaking to reporters on Friday, he remained positive about his options.
“We don’t know exactly who is available. We know about the issues with Gini and Adam, but they’re not ruled out,” he said.
“Four sessions to go, we have to see. I can wait until I make my final decision—we’ll have a really good team on the pitch.”
Wijnaldum, Lallana, Clyne and Lovren have all started every Premier League game this season when fit, magnifying their key status under Klopp.
But having travelled to South America and Africa for duty with Brazil and Senegal respectively, their availability against United came under question.
However, Klopp moved to allay these fears, saying “playing on Monday is an advantage.”
“Roberto could do a bit more [than Coutinho] in the last session,” he explained, with Firmino having played fewer minutes than his compatriot against Bolivia and Venezuela.
“Phil played two games so needed more recovery after a long, long flight.
“It’s a long trip, and it’s still in their legs, but each hour helps and playing on Monday is an advantage, of course.”
Mane returned to first-team training alongside Clyne, Lovren and another international, Divock Origi, earlier this week, so should be fit to start against the Red Devils.
Finally, Klopp confirmed that Joe Gomez had returned to training after a year on the sidelines with an ACL injury.
However, the German continued to stress that he would practice caution with the teenager’s transition back into the first team.
“It was really nice to have the boy back,” he said.
“He needs time, he has to do a lot until he’s match fit, but it’s really good.
“It’s the first time I’ve had him [in training]. It was a very nice moment.”