The 23-year-old has been persistently linked with a move to the Premier League this summer, with Swansea City, Queens Park Rangers and Arsenal among the clubs said to be chasing the Korean international's signature.
Lennon said: "I've not seen him in a month so I don't know what he's thinking at the minute. Hopefully when I see him eventually, which hopefully will be Sunday, he can let me know what he's thinking.
"They will have to pay a good fee for him. The games I watched from the Olympics, he played well.
"We could do with him coming back over the weekend and he's been made aware of that so we're hoping to see him maybe on Sunday for training."
Celtic play against Helsingborgs in the first leg of their Champions League playoff on Tuesday, August 21.