Manchester United have been unwittingly warned about the winter transfer window in the past and there are fears that they must heed to his warning or regret whatever actions they take.
The recruitment of Alexis Sanchez from Arsenal in the last winter window was the reason why the Portuguese spoke against the January transfer window after the Chile international.
Since his arrival, the former Arsenal player has yet to make any meaningful impact in the team which makes it a big loss for United having invested a lot in his weekly wages.
The former Barcelona player is now believed to want a move away from the Old Trafford with French giants Paris St Germain reported to be interested in his signature.
However, Mourinho had earlier stated that the slow start of the former Arsenal player at United is as a result of his coming to the club in the January window.
The Portuguese stressed that he joined the club in the worst moment of the season which he referred to as the winter market.
Mourinho went ahead to state that he does not like the winter market because of the desperate moves usually involved.
With United desperate to sign defenders, they could again fall in the trap of doing wrong businesses.