Once regarded as one of England’s brightest young prospects, Alli has seen his career take a nosedive in recent months.
The 24-year-old has not been included in the matchday squad in five of Tottenham’s seven Premier League games so far this season while he has only started once in the top flight.
Four of his six appearances this season have come in the Europa League and he has not completed 90 minutes in any of those games.
Alli was linked with a move away from Tottenham in the summer transfer window but a potential loan move to French champions Paris Saint Germain did not materialize.
But Dier is confident that Alli will fight his way back into Jose Mourinho’s plans as the season progresses.
"Yeah, of course 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."
