The 24-year-old started Spurs’ first Premier League game of the season but was hooked at half-time and has made just one substitute appearance in the top flight since that 1-0 defeat at home to Everton.
Mourinho recalled Alli for the side’s trip to Royal Antwerp in the Europa League last week but again hauled the England international off at the halfway stage in Belgium.
Alli has been left frustrated by Mourinho’s treatment and rumours are circling that Paris Saint-Germain could return for the attacking midfielder in January after a failed pursuit in the summer transfer window.
However, Alli’s close friend, Dier, is convinced his team-mate can turn the situation around and become a key player for the north London club once again.
‘Dele has the capacity, we all know his quality, we all know what he brings, he’s shown that in the past,’ Dier said.
‘It’s really up to him to put in the work, the effort, the commitment and I’m sure he will do that.
‘That’s who he is, he’s always had that drive. It’s up to him, it’s in his hands and it’s in all of our hands.
‘Individually, we all have to perform, we’ve got a very big squad and we all have to perform at the highest level if we want to play.’
Tottenham sit third in the Premier League table and Dier is satisfied with their start to the campaign – but feels there’s still room for improvement ahead of a busy run of fixtures for the team, both domestically and in Europe.
‘We’re happy with where we are, we could be happier,’ he added.
‘If you look at some games – the Newcastle game with the penalty, again, very difficult to understand!
‘The Everton game wasn’t acceptable and then the West Ham game the same, really frustrating to be 3-0 up (and draw 3-3).
‘It was really important for us to get off the mark at home, get the win and obviously we’ve improved massively away from home which was really our downfall last season.
‘It’s great to be up and running with a win at home and we’ll just look to keep working hard, keep pushing forward.
‘That’s a great feeling and it’s a great feeling to have. That’s the objective and the manager sets that tone from above.
‘There’s not much more I can say because we’re really focused on ourselves and we’re focused on Thursday now, the Europa League game.
‘The work with the manager has been great because you know where you stand every game and he wants to win it and the focus is completely on that. That’s his focus, no matter what the competition is. That’s always his focus and our focus.
‘Anything other than that is for others to discuss. I guess we’re just really focused in the moment.’