The English striker only has a year left on his contract and the Premier League new boys are believed to have made a bid in the region of £4.5m for his services.
Lennon revealed that the Glasgow giants want more for their top goalscorer, who scored 31 times last season.
A fee in the region of £7m would likely be accepted by Celtic's moneymen and Lennon said: "We had a bid from Hull City which we rejected. Whether they come again, I don't know. As you were.
"No set price. The offer made was well below our valuation of the player. We would be very happy for him to stay and if he decides to stay on, contract negotiations may re-open again.
"He will come to Germany on Monday and will be part of our plans for the (Champions League) qualifiers."
Lennon went on to say that discussions over a deal with out-of-contract Irish striker Anthony Stokes were ongoing and added: "He rejected an earlier offer around May time but we are hopeful we will get across the line with Anthony.
"He is a player we would like to keep."