Celtic have been linked with another full-back as they look to tie up a deal for Kilmarnock's Greg Taylor before Scotland's transfer deadline.
Boss Neil Lennon is looking for a first-team left-back following the summer departures of Kieran Tierney and Emilio Izaguirre, although he was full of praise for Boli Bolingoli's display in Sunday's 2-0 win over Rangers.
Sunderland have also made enquiries over 21-year-old Taylor, who trained with his Scotland team-mates on Monday morning ahead of their upcoming European qualifiers against Russia and Belgium.
When asked on Sunday if they could sign Taylor, Lennon said: "Hopefully. There's a bit of a hold-up, not at our end, it's a third party."
Reports claim Celtic defenders Jack Hendry and Calvin Miller could head to Rugby Park as part of the deal.
Celtic have also been linked with a move to re-sign Victor Wanyama on loan but Tottenham would prefer a permanent transfer for the midfielder, while Sunderland have been credited with an interest in out-of-favour Hoops winger Scott Sinclair.
Kilmarnock have been linked with their former midfielder, Mark O'Hara, and Scotland Under-21s forward Harvey St Clair, who is at Serie B side Venezia. The 20-year-old was in Chelsea's youth system when Killie boss Angelo Alessio was assistant manager.
Rangers manager Steven Gerrard admitted on Sunday that any new signing would have to come "out of the blue" but there could still be activity at Ibrox.
Gerrard is hoping to get players out on loan before midnight with the likes of Graham Dorrans, Jason Holt, Eros Grezda, Jake Hastie, Joe Dodoo and the fit-again Jamie Murphy out of the first-team picture.
Gerrard said on Sunday: "There could be a few out. We are trying really hard to help and support the players that want to go out on loan and play football. There could be one or two outgoings.
"In terms of incomings, I'd be very surprised, but while it's open, who knows?"
St Johnstone are looking for a left-back following Richard Foster's return to Ross County while Motherwell manager Stephen Robinson also has scope to bring a player in if he can find someone who will improve his first team.