The 18-year-old received a short-term deal after an appearance for United’s Under-21s at Thorp Arch last week and he is already training with Brian McDermott’s senior squad.
Ariyibi was raised in the USA and joined Southampton’s academy as a 10-year-old in 2005. The Premier League club released him at the end of last season and he has undergone a number of trials since, including one with Bolton Wanderers.
McDermott has been devoid of out-and-out wingers throughout his time at Leeds, and the United boss saw enough talent in Ariyibi to sign him for the rest of this term.
McDermott said: “He’s only 18 and we kind of knew him already. He played in a couple of games and took part in some training sessions and he looks like he’s got a chance. He’s quite an exciting player – very, very quick. He’s a great lad too. He really wanted to sign for us and he’s been training with the first team. He looks good.”