The 22-year-old bagged 19 goals in the Championship last season and is wanted by the Scottish giants, while Middlesbrough boss Gordon Strachan is also keen.
tribalfootball.com has learned Hoops boss Neil Lennon is willing to do business now for Hooper at £2.5 million. But Scunthorpe are refusing to budge from their £3.5 million valuation.
Hooper is inside the final 12 months of his contract and will be available on a free transfer with no training compensation if he heads north of the border next summer.
A source told tribalfootball.com: "Scunthorpe are pricing Gary out of the market at the moment. Celtic and Middlesbrough are keen to sign him but they feel his valuation is staggeringly high given his contract situation. There is a real possibility both clubs will make a new lower offer in January now."