The 19-year-old was allowed to leave Elland Road if he found a new club and he has signed a two-and-a-half year deal at Pittodrie.
Dons manager Jimmy Calderwood told his club's website: "He's only 19, but he's a good passer of the ball and has good vision for his age. I will see how he goes for the rest of the week, but all being well he might be in the squad for Sunday.
"He's got to get up to the pace of our game," he added.
"As I've said many times, Scotland is a very difficult place to play and it is quicker than England, even if they don't think so down there."