Celtic succeeded in their pursuit of Dundee United pair Stuart Armstrong and Gary Mackay-Steven in the final hours of the transfer window.
Armstrong signed a three-and-a-half-year contract in the final stages of the window while Mackay-Steven completed his move to Parkhead having already signed a pre-contract agreement. He has signed until 2019.
The move severely weakens United's attacking options just two days after they set up a Scottish League Cup final meeting with Celtic but they have the compensation of about 2 million pounds to add to their increasingly healthy finances.
United failed in a bid to re-sign midfielder Scott Allan from Hibernian but another former player, left-back Paul Dixon, returned to Tannadice from Huddersfield as Conor Townsend's loan move from Hull was brought to an end.
Celtic also signed forward Michael Duffy from Derry City and tied up 19-year-old defender Eoghan O'Connell on a contract extension that keeps him at the club until 2017.