Rojo, 30, joined United in 2014 when he was signed by Louis van Gaal, but he has long been out of the first-team reckoning.
Marcos se puso la de Boca...💙💛💙— Boca Juniors (@BocaJrsOficial) February 2, 2021
¡Muchos éxitos! pic.twitter.com/2vSbTH3oKa
But injuries and poor form saw that figure drop to nine in 2017-18 – he then featured just five times in the 2018-19 Premier League and thrice last term before he was sent to his former club Estudiantes on loan.
His brief stint back in Argentina did not go to plan either as he made a solitary appearance due to injury – he did not make a single competitive appearance for United after returning and was left out of their Champions League squad in October.
A social media post from a person stating he was Rojo's personal trainer last week appeared to lift the lid on the player's next move, claiming he was set to start training with Boca.
United have now confirmed Rojo has joined Boca for an undisclosed fee – he won four trophies during his time at the club.
"Everyone at the club would like to wish him all the best for the future," United said in a statement confirming Rojo's exit.
His final appearance for United came in November 2019, as a late substitute in the 3-1 win over Brighton and Hove Albion.