Dele Alli has only made three starts for Tottenham this season

When England's starters step out in Prague to face Czech Republic on Friday night, Dele Alli will not be among them. He will not be among the substitutes either. A player who started all three of England's knockout games at the 2018 World Cup is not in the squad this time around.

His omission, confirmed a few days before Tottenham's 3-0 loss to Brighton on Saturday, continues a difficult period for him. Mauricio Pochettino was describing Alli as the best 21-year-old in the world only 18 months ago, but he didn't even use him from the bench at the Amex Stadium and, at 23, it feels increasingly like his career has stalled.

It is little wonder that Gareth Southgate has overlooked him when he is struggling to even get a game at Spurs, let alone make an impact. Since his return from injury at the start of September, Alli has only featured in four games out of eight. The three he has started - against Olympiakos, Colchester and Bayern Munich - have all ended in disappointment.

Those disappointments aren't all on Alli, of course. He is not the only Spurs player struggling. But it has been some time now since he has produced his best form on anything like a consistent basis. Since 2016/17, when he scored 18 Premier League goals in 37 games, winning his second consecutive PFA Young Player of the Year award, he has only hit 14 in 62.

He has not added to that tally since January, and it is not just the goals that have dropped off. His numbers for dribbles, shots and key passes are all trending downwards. Last season, he averaged fewer per 90 minutes than in any of his previous three campaigns with the club.

Alli is no longer playing to his strengths, in other words, and it is partly down to the changing make-up of this Spurs side. Last season, as Heung-Min Son's importance grew and Lucas Moura joined him in support of Harry Kane, Alli was moved from his attacking midfield role into a deeper one.

He has previously said he sees his future in that position, but by placing him in the heart of the team, you are taking him further away from the areas in which he is most dangerous, areas in which he can chase down opposition defenders and ghost into the box to finish off chances.

Dele Alli in action against Arsenal earlier this season

That's certainly what he did during that brilliant 2016/17 campaign, his natural scoring ability evident in the sheer variety of his goals. His total that year included five with his weaker foot, four with his head and one effort from outside the box. Premier League defenders could not cope with him.

Have injuries taken a toll?

Alli only missed three Premier League games out of 76 between the start of that season and the end of the subsequent one, but injuries have become a problem since then. Indeed, while some have asked questions of his focus, it's the issues with his left hamstring that have most obviously hampered his progress.

Most notably, there was the tear he suffered during Tottenham's 2-1 win over Fulham at Craven Cottage in January, the night he scored what remains his last goal for the club.

Dele Alli spent six weeks on the sidelines after injuring his hamstring in January

Spurs were already without Kane at the time. It felt like an opportunity for Alli to fill the void. But suddenly he was ruled out for six weeks and, in his absence, Son stepped up instead, scoring four valuable goals in his next four appearances to further emphasise his status as Pochettino's go-to man after Kane.

Alli went straight back into the Tottenham team on his return to fitness, starting 13 of their final 14 games of the campaign, including the Champions League final, but a recurrence of the problem in August came as another setback. "We are worried," conceded Pochettino. "He is still only 23 and has had many hamstring problems in the last few years."

The injuries are far from ideal for a player reliant on hard-running and explosive bursts of speed, and his lengthy absences have also impacted his on-field understanding with his team-mates.

1:09 Mauricio Pochettino insists he still believes in Tottenham Mauricio Pochettino insists he still believes in Tottenham

His link-up play with Kane, once a major strength for Tottenham under Pochettino, seems to have been lost. In the recent Champions League meetings with Olympiakos and Bayern, during which Alli and Kane spent 144 minutes on the pitch together, they only exchanged passes five times - and that despite Alli starting in advanced positions in both games.

Spurs supporters are still with him. His name could be heard reverberating around the Tottenham Hotspur Stadium just two minutes into the game against Bayern and there were loud cheers for him when he chased down right-back Benjamin Pavard soon afterwards. In the end, though, he left the field in the second half having once again struggled to impact the game.

Alli has time on his side having only turned 23 in April - while Pochettino has said he has "no doubts" that he will recapture his best form - but time is not a luxury Spurs can afford at the moment. The pressure is already mounting after their dismal start to the season.

Dele Alli featured in Tottenham's 7-2 thrashing by Bayern Munich

They need Alli back at his best but in order to get there he must first win back his place in the side. Son and Moura are ahead of him in the attacking pecking order and, in summer signings Tanguy Ndombele and the Giovani Lo Celso, Pochettino has fresh options in midfield too.

At international level, the competition for places is even stiffer, with James Maddison and Mason Mount now pushing for a spot in Southgate's midfield and rising stars Jadon Sancho and Callum Hudson-Odoi hoping to establish themselves further forwards.

It is down to Alli, then, to show how he fits into it all. In some ways, he has become a victim of the high standards he set for himself in those brilliant early years at Spurs. But he has never seemed further from meeting them than he does now. The sooner he can kick-start his career, the better.

Follow England's European Qualifier against Czech Republic on the Sky Sports live blog on Friday from 6pm; Kick-off 7.45pm