Manchester United announced they had signed Bayern Munich midfielder Marcel Sabitzer on loan in the early hours of Wednesday.
United were forced into deadline-day action on Tuesday following an ankle injury to Christian Eriksen, which is set to rule the Denmark midfielder out until early May.
Manager Erik ten Hag completed the loan signing of Netherlands forward Wout Weghorst earlier in the January transfer window.
Sabitzer, 28, who was previously club captain of RB Leipzig, has won 68 caps for Austria.
"Sometimes in life you have to make quick and important decisions," said Sabitzer, who will be at Old Trafford for the rest of the season.
"From the moment I heard about this opportunity I knew it was right for me. I am a competitive player -- I want to win and help the club achieve its aims this season.
"I feel that I am at my peak as a player, and that I can contribute a lot of experience and energy to the squad."
Manchester United football director John Murtough said: "Marcel is a player that we have watched for a long time. The opportunity arose quickly, and we knew that he was someone with the ability and character to make an impact."
United are fourth in the Premier League and are hot favourites to reach next month's League Cup final.