Celtic turned down a bid from Norwich City for the 25-year-old earlier this year, with several clubs being linked to a move for Hooper during the current transfer window.
The Hoops manager told the Daily Record: "We knocked back £6m for him in January so we won't be bullied by big-money offers for any of the players.
"We have a team full of prized assets here. We're comfortable with our valuations and if they are not met we are not in any desperate need to sell them.
"But Gary has been brilliant. I haven't seen a change in attitude at all from Gary and I haven't had to speak to him."
Hooper scored 31 goals in 51 games for the Scottish champions last season.