A 2-0 win over Manchester City on Saturday moved Spurs top of the Premier League and sent a statement to their title rivals.
It was the perfect way for Mourinho to celebrate a year in charge at the club and despite continued scepticism over his tactics at times, the Portuguese watched his side produce a trademark disciplined display and gain reward at the weekend.
"Three clean sheets in our last four and Toby's been a big part of that. I thought again he made some fantastic interceptions, tackles, blocks when he needed to.
"Obviously any player in this squad getting injured is a big loss for us and Toby's no different."
It could open the door for young Welshman Joe Rodon, who replaced Alderweireld late on against City.
When he signed for Spurs in October, it was after they had registered their Europa League squad and he will therefore miss Thursday's home tie with Ludogorets, but could be handed a full debut away to Chelsea on Sunday.
Dier said: "He's very humble, very hard-working. From what I can see he has a fantastic mentality to want to work, to improve.
"From what I've seen around the training ground, all of those things have been fantastic and I know the Welsh boys Ben (Davies) and Gareth (Bale) speak very highly of him, so excited for him to be able to help the team."