Jose Mourinho admitted striker Harry Kane's injury is as bad as he feared after seeing Tottenham held to a 1-1 FA Cup third round draw at Middlesbrough.

Kane damaged a hamstring in the 1-0 Premier League defeat at Southampton on New Year's Day and although his manager does not yet know how long the England captain will be sidelined, it appears he could face an extended spell out.

Mourinho said: "I think it is better for the medical department to speak about it or make an official report.

"The only thing that I can add is that the feelings I had that it was not a small injury were correct. It is not a small injury, but I cannot speak about times."

Kane's absence was noticeable as Spurs struggled to break down a well-organised Boro at the Riverside Stadium, with Son Heung-min and Lucas Moura attempting to plug the gap.

It was Moura who eventually cancelled out Ashley Fletcher's 50th-minute opener with a firm header, but the Portuguese was disappointed his side did not make more of their share of possession, although he refused to use Kane's misfortune as an excuse.

Mourinho said: "I didn't speak – or if I did, it was very occasionally – about [Hugo] Lloris. I am not coming here, or to press conferences pre-match, you never hear me, 'Lloris, Lloris, Lloris', so in this moment, it is not going to be 'Harry, Harry, Harry, Harry'.

"We have what we have and we stick with them. The boys did what they can. You cannot transform Lucas or Son into a number nine like Harry Kane, so we have to try other things and that is what we are going to do.

"While Harry is out, obviously every minute he doesn't play means a lot to us. It is a big loss for us, but we have to accept it and we have to fight with the boys that are available."

Boro boss Jonathan Woodgate had nothing but praise for his players, who went into the game on the back of four Sky Bet Championship wins.

Woodgate said: "Wins bring confidence and OK at times this season we've maybe been lacking that with a few of the results.

"But we've stayed with it and we haven't been that far away home and away and we've had some good performances – and again that was a really good performance."