Winger Gary Mackay-Steven has joined Aberdeen from Celtic on a two-year contract.
And the 26-year-old goes straight into the squad to face Siroki Brijeg in Thursday’s first leg of their Europa League second qualifying round tie.
The two clubs had been apart in their valuation of the player earlier this week before an agreement was reached.
Manager Derek McInnes had said earlier in the day that he had hoped to add to his squad before the game at Pittodrie.
Clubs are allowed to make one ‘wild card’ signing on the day prior to qualifying ties.
Mackay-Steven travels in the opposite direction to Jonny Hayes, the Republic of Ireland winger who switched from the Dons to Celtic Park for £1.3m this summer.
He joins a squad containing former Celtic team-mate Ryan Christie, whose presence on a second season-long loan from the Scottish champions meant a permanent transfer was necessary if Mackay-Steven was to move to the Granite City.
Scottish Premiership rules bar more than one player being on loan from a rival club.
Mackay-Steven’s switch came hours after Celtic confirmed the signing of midfielder Olivier Ntcham from Manchester City for a fee of about £4.5m.
McInnes has now made five summer signings as he looks to compensate for the loss of six first-team regulars.
Mackay-Steven, who started only five games for Celtic last season, will be viewed as a replacement for Hayes and Northern Ireland forward Niall McGinn, who rejected the offer of a new contract to join Gwangju in South Korea.
An attempt to sign Scotland international Shaun Maloney from Hull City had stalled after the 34-year-old attacking midfielder flagged up an injury problem.
A bid for Stevie May also fell foul of Simon Grayson’s departure from Preston North End to Sunderland, with new manager Alex Neil saying he wanted to give the former St Johnstone striker a chance to win a regular first-team place following injury problems last season.
Mackay-Steven, who made a total of 10 appearances last season, joined Celtic in 2015 after rejecting a new contract with Dundee United.
The winger, who has one Scotland cap, was with Ross County, Liverpool and Fulham as a youth but made his senior debut for Airdrie United before moving to Tannadice.