Robbie Neilson said the opportunity to sign Marcus Tavernier on loan prompted him end Gboly Ariyibi's deal at MK Dons.
Tavernier joined on loan from Middlesbrough until the end of the season, while Ariyibi, who was due to remain at Stadium MK until June, returned prematurely to Nottingham Forest on Wednesday.
Ariyibi is the second player to have his loan deal terminated, after Aaron Tshibola was sent back to Aston Villa in November, while Scott Golbourne's loan from Bristol City ended on Saturday after he required hip surgery.
Neilson said: "With the Gboly situation, we knew with Marcus coming in we felt it better that Gboly went back. We all agreed about it. There were never any issues with Gboly's commitment but sometimes you need freshness coming in.
"It has been a difficult season for us, and at times when players come in on loan it can be difficult for them.
"We have been looking at Marcus for a while now, so made some enquiries about him and were lucky enough to get him. He'll give us some energy in there. He'll give us a lift. He brings energy, work rate, pace. He's good at driving forward in midfield, and will fit in well with the group."