Bolton Wanderers have signed Celtic midfielder Filip Twardzik for an undisclosed fee and Sporting Lisbon midfielder Simeon Slavchev on loan.
Czech youth international Twardzik, 21, who joined Celtic alongside twin brother Patrik in 2009, has agreed a deal until 2017.
He played for the Hoops under Trotters boss Neil Lennon.
Bulgaria international Slachev, 21, will stay with Bolton until the end of the season.
He joined Portuguese side Sporting from Litex Lovech last summer.
The pair take the number of arrivals at the Macron Stadium in the January transfer window to five, after the signings of goalkeeper Ben Amos, striker Adam Le Fondre and midfielder Rochinha.