Celtic signed forward Michael Duffy from Derry City in a deal worth a reported £100,000 in the final stages of the transfer window last night.
The Scottish club also succeeded in their pursuit of Dundee United pair Stuart Armstrong and Gary Mackay-Steven.
Armstrong signed a three-and-a-half-year contract while Mackay-Steven completed his move to Parkhead having already signed a pre-contract agreement. He has signed until 2019.
The move weakens United's attacking options just two days after they set up a QTS Scottish League Cup final meeting with Celtic but they have the compensation of about £2m to add to their increasingly healthy finances.
And, after failing to re-sign Scott Allan from Hibernian, they used some of that money to buy Scotland Under-19 forward Robbie Muirhead from Kilmarnock on a three-and-a-half year deal.
Left-back Paul Dixon returned to Tannadice from Huddersfield as Conor Townsend's loan move from Hull was brought to an end.
and tied up 19-year-old defender Eoghan O'Connell on a contract extension that keeps him at the club until 2017.
Donervon Daniels (West Brom, loan), Joe Shaughnessy (Falkirk, end of loan), Kenny McLean (St Mirren, undisclosed), Lukas Culjak (Borussia Dortmund, free)
Jeffrey Monakana (Brighton, end of loan), Declan McManus (Morton, loan)
Michael Duffy (Derry City), Stuart Armstrong (Dundee Utd, undisclosed), Gary Mackay-Steven (Dundee Utd, undisclosed)
Amido Balde (Hapoel Tel Aviv, loan); Beram Kayal (Brighton, undisclosed fee); Jo Inge Berget (Cardiff, end of loan)
Kostadin Gadzhalov (Dobrudzha Dobrich, free); Alex Harris (Hibernian, loan), Stephen McGinn (Sheffield Utd, free), Paul Heffernan (Hibernian, free)
Martin Boyle (Hibernian, loan), Arvid Schenk (released), Peter MacDonald (Morton, free), Dylan Carreiro (Arbroath, loan), Phil Roberts (Alloa, loan)
Ryan McGowan, (Shandong Luneng Taishan, free), Henri Anier (Erzgebirge Aue, undisclosed), Simon Murray (Arbroath, £50,000), Robbie Muirhead (Kilmarnock, undisclosed)
Simon Murray (Arbroath, loan), Keith Watson (Hibernian, loan), Mark Wilson (released), Stuart Armstrong (Celtic, undisclosed), Gary Mackay-Steven (Celtic, undisclosed), Conor Townsend (Hull, end of loan)
Lee Lynch (Limerick, free), Nico Sumsky (Dukla Bystrica)
Alex Neil (Norwich, undisclosed), Mickael Antoine-Curier (released), Tony Andreu (Norwich, £1million)
Billy McKay (Wigan, undisclosed fee), Ibra Sekajja (released)
Robbie Muirhead (Dundee Utd, undisclosed)
Anthony Straker (York City, loan), Stephen Pearson (Kerala Blasters, free), Louis Long (Nottingham Forest, loan), George Long (Sheffield Utd, loan), Conor Grant (Everton, loan), Marvin Johnson (Kidderminster, undisclosed), Nathan Thomas (Plymouth, free)
Henrik Ojamaa (Legia Warsaw, end of loan)
Callum Booth (Hibernian, loan), Ryan Finnie (Rangers, free), Lyle Taylor (Scunthorpe, loan)
Aaron Muirhead (Falkirk, free), Nathan Eccleston (released)
Darvydas Sernas (Wigry Suwalki, undisclosed), Marcus Fraser (Celtic, free), Cameron Burgess (Fulham, loan), Craig Curran (Nuneaton Town, free), Ruben Palazuelos (Ermis, free), Rafa de Vita (Cheltenham, free)
Yoann Arquin (St Mirren, free), Lewis Toshney (released), Darren Maatsen (released)
George Hunter (Spartans, undisclosed), Danny Swanson (Coventry, loan)
Gary McDonald (released)
Yoann Arquin (Ross County, free), James Dayton (Oldham, loan), Emmanuel Sonupe (Tottenham, loan)
James Marwood (Forest Green Rovers, free), Ross Caldwell (Morton, free), Adam Drury (Manchester City, end of loan), Ellis Plummer (Manchester City, end of loan), Kenny McLean (Aberdeen, undisclosed)