Striker Montano joined the League Two Robins on a one-month deal in October and scored on his debut in a 2-0 win at Accrington.
But things soon turned sour and legendary former Hammers frontman Di Canio revealed last week he had been unimpressed by the 19-year-old's attitude in training.
Di Canio said he would not be picking Montano in Tuesday night's Johnstone's Paint Trophy clash with AFC Wimbledon, although he did offer him the chance to prove he wanted to stay at the County Ground.
Montano was due to return to Upton Park after the clash with the Dons.
But Montano was on Tuesday afternoon back with the Hammers and played in their development squad game at Gillingham.