The 24-year-old England global sat out Wednesday's 3-2 EFL Cup loss to West Ham and Tottenham confirmed the injury via a brief statement on Twitter. "It's lucky it's not a big problem but he's not going to play tomorrow".
In a briefing with the press, Mourinho said that people should not talk to him about Harry Kane's injury yet he has to play without French midfielder Paul Pogba, Belgian powerhouse Marouane Fellaini, veteran Michael Carrick and injury-prone Argentinian Marcos Rojo.
"It is a collective sport and always you must adapt when some player is not fit to play".
"I'm disappointed because he is our main striker and I think he is one of the best strikers in Europe, in the world, and always you are going to miss your best striker". In this type of game, if you make a mistake, you pay and lose.
'We went into the game believing we could win. I think last season, in the period he was injured, you can see the stats and the games we played - win and lose with Harry, win and lose without Harry. This won't be the cautious United we saw in the 0-0 draw at Liverpool. The players are not machines and it is so hard to cope with worldwide duty and playing every three days. Pochettino said it was only a "small issue" but he did not want to exacerbate the problem by playing him against United.
"It will be a big statement if we beat them". "We will see tomorrow and the day after", he said.
Mauricio Pochettino selected Son Heung-min in attack rather than Fernando Llorente and Spurs made good progress in wide areas in the first half, where they lacked Llorente's physicality, and then seemingly abandoned the tactic once the Spaniard was brought on in place of Son just after the hour.
"It was a very, very, very competitive game", he added.
"He needs two, three, four, five or six matches in a row to play, to make mistakes, to get conditioned, to get match fitness and I can not give him that".