After an impressive first season at White Hart Lane, the midfielder improved in 2015/16. He scored 18 goals and registered seven assists to cement himself as one of the world's brightest young players.
But in 2017/18 he failed to hit the same heights and dropped back to the level of his debut season at Spurs. So what happened?
For a start, it’s worth mentioning that scoring nine and assisting ten goals – as he did last term and did the reverse in 2015/16 – is an impressive feat. Very few players manage it per season and there are four Premier League campaigns where nobody managed it at all.
So for Alli to get close not once, not twice, but three times in a row, at such a young age, shows what kind of a talent he is. But let's investigate that drop-off…
The drop-off and a change in role
So why did Alli's goal output halve from 2016/17 to 2017/18? Basically, he stopped hitting the target as much.
His rate of shots which tested the opposition goalkeeper dropped from 47 per cent to 25 per cent between the two seasons.
The number of chances he was getting per game stayed roughly the same – as well as the quality of them – it's just that he lost that special ability to find the back of the net.
In terms of his all-round game, Alli played similarly in the two years, as seen by his Football Whispers player persona radar, which looks at how a team or person’s plays stylistically.
But the current campaign, one which has been disrupted by a persistent hamstring injury, is going slightly differently.
Alli hasn't claimed an assist this term and the numbers suggest that, when he returns to the side, that is unlikely to change anytime soon.
The amount of shots he’s setting up has dropped from 1.6 per 90 minutes last season to 0.5 per 90. Instead, the 22-year-old seems to have taken on extra responsibility in attack and in defence, leaving out the creativity in the middle.
Alli’s defensive activity has absolutely leaped this season, more than double what it has been in the past two campaigns with 4.96 tackles and interceptions per 90 minutes.
His touches inside the opposition box have also jumped, from just under five per 90 minutes in those previous years but nearly seven per 90 this campaign. He’s even receiving more passes inside the box than Harry Kane.
It’s a curious role and not one many players are probably tasked with which, in turn is perhaps why the public enthusiasm around him has died. How are we supposed to measure success in this role that we’ve not really seen before?
The fact that he’s making fewer shot assists and not taking any more shots than last season, despite getting more touches in the opponents’ box, doesn’t seem like a sign of success.
He’s still an important part of Mauricio Pochettino’s side moving the ball up the pitch, but Alli is one of the players where end product is supposed to come from.
With Kane struggling earlier in the season, Spurs fans could reasonably have hoped that the 22-year-old would step up and fill some of that void.
But whether Alli gets back to the eye-catching heights of the past few years, 2016/17 in particular, will depend on whether Pochettino continues to play him in this role.
Such a heavy defensive responsibility, be it relentless pressing or more conventional defensive work, won’t make attacking end product any easier to come by.
But defending is a thankless task, for the most part, and perhaps we should all recognise the task that the midfielder has had to perform this season.
There’s still a lot of time in the campaign and his career for Alli to get back to his best. He’s shown that he can do it before and, if given the opportunity, he’ll be able to do it again.