Celtic could make a fresh bid for Sheffield United defender George Baldock, despite having a reported £3 million offer turned down earlier this summer.
Neil Lennon is in the market for a right-back having seen Cristian Gamboa, Mikael Lustig and Jeremy Toljan depart during the summer.
Kristoffer Ajer, ostensibly a centre-back, operated at full-back against FK Sarajevo on Tuesday night with midfielder Nir Bitton deployed as Jozo Simunovic's partner at the heart of defence.
The Hoops were linked with Tommy Smith but the Huddersfield defender looks to be on his way to Stoke City.
Meanwhile, Celtic are reportedly keeping tabs on Middlesbrough forward Britt Assombalonga, but could face competition from a host of other clubs.
The DR Congo international has been Boro's top scorer in his two seasons at the Riverside following his £15 million switch from Nottingham Forest in the summer of 2017.
Lennon is understood to be keen on beefing up his attacking options, with just Odsonne Edouard and Leigh Griffiths, who is still getting back up to speed following an absence, as his first-team strikers.