Son scored twice –including the winner– as Mourinho’s men moved to fifth on the table, just a point behind Chelsea in the race for fourth place.
A statement on Tottenham’s website on Tuesday read: "Following surgery, our medical staff shall be reviewing management options for Son's rehabilitation with the player expected to be sidelined for a number of weeks."
However, Mourinho feels Son might be out for longer than just ‘a number of weeks’.
“Simon [the press officer] found a very nice way to write the statement but if I was to write the statement, I'd write something different,” the Portuguese told reporters prior to the first leg of Spurs' Champions League last-16 clash with RB Leipzig on Wednesday.
“So we'll miss him, according to Simon, for a number of weeks.
“I'm not going to count on him again this season. If he plays two or three games then it's because he (Simon) is very optimistic, but I'm not counting on him.”
Tottenham were already without the services of Harry Kane, who has been sidelined till April, and Son has filled in superbly in the Englishman’s absence, scoring in each of his last five games.
The South Korean international has played 32 games this season, scoring 15 goals.