Brendan Rodgers has warned clubs that in-demand midfielder Matt O'Riley will not be leaving Celtic on the cheap, telling them to "value the player, not the league."
The Scottish Premiership champions have rejected three bids for the midfielder from Atalanta, with the latest offer believed to be a £15m initial fee, plus add-ons.
Atalanta's Serie A rivals Juventus and Roma, plus La Liga side Atletico Madrid have also shown an interest in the Denmark international who scored 19 goals with 18 assists in 49 appearances for Celtic last season.
O'Riley captained the Hoops in their 4-0 pre-season win over DC United in Washington last Sunday and Rodgers has been delighted with his attitude amid continued interest.
"It's been actually straight forward with Matt because he's such a great professional," he told Sky Sports News.
"The challenge for teams coming to a club like Celtic is they sometimes can place their value on the league and not the player.
"Obviously there are riches in other leagues much greater than ours that allows players to go and improve their conditions for their life, we all understand that.
"What's important for me is if a player does leave here they pay the value for the player and that isn't something that always happens.
"No player will leave here unless it's for the right valuation and at this moment in time there's been no team that's been anywhere near that."
Goalkeepers Kasper Schmeichel and Viljami Sinisalo are Celtic's only summer signings so far, with the club's initial bid for Norwich striker Adam Idah rejected.
"We still have work to do. In transfers there are a lot of moving parts, it's never as easy as seeing a player and just bringing them in but we'd hope by the end of August that we would have the team supported who we want it," the 51-year-old added.
"You cannot snooze in this game of football, you always have to be developing and improving. We want to ensure we have an improved squad for this season to take on all the challenges that we have.
"Everyone would love to get their work done as soon as they can. We would love to have had everything done for the first game of the season but that doesn't always end up being the case.
"My hope is we can be much stronger coming out of the August window than what we finished last season.
"Adam is obviously a Norwich player. I had said he'd done fantastic with us last season [on loan] and we'll just see what happens over the coming weeks."
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