The 19-year-old has scored three goals for the Magpies since joining on an initial one-month loan deal August which was then extended by a further month.
"It's important to let all our supporters know that today [Sunday] will be Cristian Montano's last game for Notts County," Allen told the club's official website.
"I was told on Friday afternoon that he has been recalled by West Ham to go into their first-team squad.
"He's been a model professional. Down to earth, humble and hard working.
"He's very popular with the staff and players and this afternoon I hope all our supporters give him a fantastic finale."