On Thursday Celtic turned down a £5million bid from Norwich City for the striker that they rate at twice that price.
Norwich are expected to return with an improved offer as Chris Hughton attempts to add fresh firepower to his side with other clubs watching the situation closely.
Hooper is out of contract in June 2014 but no-one at Celtic expects him to be in Scotland at the start of next season after resisting attempts to extend the contract he signed as a €2.5m signing from Scunthorpe in July 2010.
With over €20m pouring into the club from the Champions League campaign Celtic don't have to sell Hooper to balance the books but Lennon appreciates the reality of the situation and the opportunity for the striker to take his wages into the €50,000 a week bracket in the English Premier League.
"I am not going to stop any of the players' progress because I wouldn't have wanted that done to myself," the Celtic boss explained. "But I'll do what I think is in the club's best interests.
"I don't think he's far away from England recognition. I don't have a set figure but goalscorers are at a premium. We'll set the bar pretty high for Gary.
"In the short-term future it is about keeping Gary here. The last week of the window gets pretty heavy. I am sure he's on the radar of plenty of clubs. It is just Norwich have come in first.
"I have made it clear, Peter Lawwell (Celtic's CE) has made it clear and the board have made it clear we are not selling him.
"However, everyone has their price. What Gary's price is will be down to myself and the board to decide if a club comes up with that figure. What we were offered on Thursday was nowhere near our valuation."
On the park, Georgios Samaras and Lassad Nouioui joined Hooper on the scoresheet in the 4-1 win over Hearts at Parkhead.
Anthony Stokes was an unused substitute and is expected to play in tonight's reserve match against Motherwell.