The Hoops have seemingly had to rethink their transfer strategy for this window.
Ronny Deila has admitted to Norwegian website VG to being frustrated that despite Celtic's stature in the European game, they are unable to compete with some English sides that are playing in the Championship.
The Hoops may be six points clear at the top of the Scottish Premiership, have great opportunities to win both domestic cup competitions, and regularly find themselves competing for, or earning a place, in the Champions League, but Deila explained that that is still not enough for some players when they hear that clubs south of the border are interested, even if the side chasing their signature plays in the second tier.
"It gets harder and harder to get hold of good players. England destroys the market," Deila told VG.
"A club like Celtic is enormous in Scotland, but we can't compete with clubs in the English Championship for players now."
The struggles to bring in players has seemingly caused the Bhoys to rethink their strategy during this window, to now often look towards players who play their club football in Eastern Europe.
Recently, Celtic have been linked with the likes of Ljuban Crepulja of Slaven Belupo (via Daily Record) and HNK Rijeka's Ivan Mocinic (via Daily Record), while also handing a trial to Romanian right-back Andrei Peteleu (via Evening Times).
Targeting largely lesser known players may result in Celtic recruiting fewer household names, but it should also mean that they are able to sign talented players who have yet to fully develop a reputation in one of the continent's major leagues, and thus, their value may be lower.
While that strategy is likely to see the club uncover some real bargains - like they arguably have with the likes of Nir Bitton and new arrival Erik Sviatchenko - it also means that the scouting team has to work much harder to find good players, before deciding whether they would actually improve Celtic's squad.