Sunderland have signed winger Romaine Mundle from Standard Liege on a four-and-a-half year deal, while Barnsley midfielder Callum Styles joins on loan.
Mundle, 20, left Tottenham to join the Belgian top flight side last summer and has played six league games for them.
He never made a senior appearance during his time at Spurs.
Meanwhile, Sunderland have the option to make their deal for 23-year-old Hungary international Styles permanent at the end of the season.
Styles, who has made 151 appearances for Barnsley, told the Tykes during the transfer window that he wanted a winter move to play at a higher level this season.