Lennon, talking in Sweden after Celtic arrived in preparation for their match with Helsingborg, claimed the length of Ki's contract meant a potential windfall of £6million could not be ignored.
He said: "We are in advanced discussions with a club at the minute and we are hoping the deal will go through.
"I am not at liberty to say (if it's Swansea) but there may be interest from other clubs as well.
"He is not here, we have given him a bit of extra time because he has a lot to think about.
"He has only 15 months left on his contract and we feel it is a good offer and good business on our side."
The Celtic manager also admitted the policy at the club seemed to be heading in the direction of signing young players for small fees and developing them to earn a profit.
"It is unfortunate to lose a quality player," he said.
"But that has been our strategy at the club for the last two or three years, cultivate these players and eventually move them on if they want to go."