Mourinho was asked about the England international's fitness in a pre-match press conference and said he is unsure when he will be fit enough to return to action, per the Guardian's Nick Ames.
"We try the best we can. News on Harry we don't have, and if you ask me every time we come here the answer will be the same. We expect him to be out until mid-April, end of April, May, next season, I don't know."
Kane has since taken to social media to confirm he has gone under the knife and is now on the road to recovery:
The 26-year-old will clearly be a big miss for Spurs as he is the club's main source of goals. He has netted 17 times in all competitions for the north Londoners in 25 starts this season and is the club's record Premier League goalscorer:
Mourinho's comments are also likely to concern England manager Gareth Southgate. The Three Lions kick off their UEFA Euro 2020 campaign on June 14 against Croatia at Wembley Stadium.
Kane has 32 goals in 45 England appearances and his absence would hurt England's hopes of winning the tournament for the first time. The striker netted 12 goals in eight matches in qualifying and won the Golden Boot at the FIFA 2018 World Cup.
England do have a wealth of options in attack with players such as Marcus Rashford, Raheem Sterling, Jadon Sancho and Tammy Abraham all available.
Yet none possess Kane's experience, leadership and goalscoring ability which Southgate will view as crucial to his team's hopes of success in the summer.