Celtic are interested in signing Aberdeen centre-back Scott McKenna and could make a bid before the transfer window closes at the end of the month.
The Dons have no inclination to sell the Scotland defender, who is currently recovering from a hamstring injury.
McKenna, 21, has won four international caps since his debut in March and captained Scotland in Mexico in June.
Celtic are keen to strengthen their defensive options, with Dedryck Boyata's future still uncertain.
Aberdeen rejected three bids from Hull City in January for McKenna, who signed a contract extension on improved terms in March this year, running to 2023.
Swansea were also believed to be interested in the player before the English transfer window closed earlier this month.
Celtic have yet to make a bid, but Aberdeen are bracing themselves for a fresh offer before 31 August for a player who had loans spells at Ayr United and Alloa Athletic before establishing himself as a first-team regular last season.
McKenna played in both legs of Aberdeen's Europa League tie with Burnley but suffered a hamstring injury in their opening Premiership game against Rangers, which will keep him out until next month.
'He's one for the future' - analysis
Former Celtic forward Kris Commons on BBC Radio Scotland's Sportsound
He would be a good addition. Celtic have been crying out for a good centre-half for 12-18 months now.
He's not had a great deal of football, four international caps. At the minute, he's one for the future. In 12-18 months you'll probably see the best out of him. He's on a long-term deal as well so he's in no rush.
Celtic are crying out for a finished article centre-half. Celtic sign players for £2m, £3m, £4m tops. Olivier Ntcham was £4.5m. Other than that you've got Odsonne Edouard, they broke the bank for that one at £9m.
They ain't going to be paying £8m, £9m, £10m for a centre-half that's 21 that was playing for Ayr United last season. He got his experience at Ayr and Alloa but this is a guy that's played 30-plus games for Aberdeen. He's not played 300 games in competitive football.