Mauricio Pochettino is baffled by the Uefa regulations that have put the squeeze on his Champions League squad and resulted in him having to omit Érik Lamela for the group phase of the competition.

The Tottenham Hotspur manager, who is preparing for the opening tie against Borussia Dortmund at Wembley on Wednesday night, cannot believe that the England international Eric Dier is considered to be a foreign player. As such, Dier must take up one of the 17 places in the 25-man senior squad that are allocated to non-locally trained players.

Dier was born in England but he emigrated to Portugal with his family when he was seven and he was raised there. He also counts as a non-homegrown player in Tottenham’s Premier League squad.

What has tied Pochettino’s hands in Europe – and resulted in the misfortune for Lamela, whom the club hope will be back from his long-term injury lay-off in November – is that the Wales international Ben Davies is another who is not considered to be a locally trained player.

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Davies counts as homegrown in the Premier League but not in Uefa competition, where association-trained players must have been “registered with a club or with other clubs affiliated to the same association as that of his current club for a period, continuous or not, of three entire seasons or of 36 months” between the ages of 15 and 21. Davies served his apprenticeship at Swansea City and they come under the Football Association of Wales rather than the English FA. And yet, as Pochettino can ruefully point out, Swansea play in the English league.

Uefa reserves a minimum of eight places in a club’s senior squad for locally trained players and, of that number, no more than four can be association-trained. Club-trained players – who have been developed by that club – are the other category of locally trained player.

Pochettino has been further restricted by the fact that his summer signings, Davinson Sánchez and Juan Foyth, do not count in Uefa competition as under-21 players – as they do in the Premier League. It has meant that Pochettino has had to accommodate them among his 17 non-locally trained senior players. Uefa stipulates that an under-21 player must have been “eligible to play for the club concerned for any uninterrupted period of two years since his 15th birthday by the time he is registered with Uefa”.

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The discrepancies over Davies, Sánchez and Foyth meant that Pochettino could not include Lamela or Vincent Janssen among his 17 non-locally trained players for the Champions League. Janssen has since been loaned to Fenerbahce for the remainder of the season but Pochettino would have liked to have had Lamela as an option.

The winger has been out since October last year with hip problems but Pochettino says that he expects him to be back in training with the squad in early October which would, hopefully, see him back in action some time in November. Tottenham’s penultimate Champions League group stage tie is at Dortmund on 21 November. Their final one is against Apoel Nicosia at Wembley on 6 December. Clubs are permitted to make changes to their squads for the knockout rounds that start in February.

Pochettino said: “It’s true that our problem was to have had 19 players that did not count as home-grown for the Champions League squad [including Lamela and Janssen]. It’s unbelievable that Eric Dier is not home-grown when he’s playing for England. That is so strange, no? It kills a little bit our possibilities.”

Tottenham’s Champions League senior squad: Goalkeepers Lloris, Vorm, Gazzaniga. Defenders Trippier*, Aurier, Alderweireld, Vertonghen, Sánchez, Foyth, Rose**, Davies. Midfielders Dier, Dembélé, Wanyama, Eriksen, Sissoko, Nkoudou. Forwards Kane**, Alli*, Son, Llorente

NB – Winks & Walker-Peters count as under-21 players; *Association-trained player; **Club-trained player