Swansea boss Carlos Carvalhal says he was assured when he took the job that key players would not be sold.
He said: "When I signed it was very clear that we would try and bring in players to improve the team, and will not sell the best players in January. So, the message is clear."
Asked if he had been guaranteed that Mawson would not be sold, the Swansea boss added: "Yes, of course.
"[But] If someone comes and gives 100 or 50 millions, of course it is completely different.
"We never can say that it will not happen but the fundamental idea is not to sell players but to try and improve the team."