Celtic made it six signings in little over 24 hours ahead of Wednesday night's UEFA registration deadline.
The Hoops brought in four loan players ahead of their 3-0 win over Aberdeen and confirmed the arrivals of 19-year-old midfielder Joel van den Berg from PSV Eindhoven and Swiss right-back Jordan Lotomba soon after the game.
Danish midfielder Oliver Sorensen and Chelsea striker Shim Mheuka made their debuts off the bench in the Scottish Premiership clash.
Wolves goalkeeper Sam Johnstone was also among the substitutes while a second 18-year-old Chelsea player, left-back Landon Emenalo, also signed but is several weeks away from fitness.
Van den Berg then arrived on a four-year deal while 27-year-old Lotomba has signed until the end of the season.
Both signings were completed just ahead of the UEFA registration deadline of 11pm on Wednesday.
The Hoops had been linked with a move for Torino midfielder Gvidas Gineitis but failed to land the midfielder.
Celtic freed up further space in their squad on Tuesday night with the permanent departures of Johnny Kenny and Reo Hatate to Preston and Burnley respectively.
Speaking after the win over the Dons, manager Martin O'Neill said of Celtic's late arrivals: "I'm very pleased that they're in the door. I think that they'll definitely add something to us.
"Honestly I am pleased, the transfer window is there and I'm pleased that we have done what we have because there's quite a few who have left the football club.
"Reo's gone and Johnny Kenny has gone, I wish them all the best."
The six new arrivals in September follow the earlier summer signings of Camilo Duran, Kasper Hogh, Mika Baur and Haissem Hassan.
