Thomas Frank has warned Mathys Tel he will not let him leave Tottenham this month.
Tel was upset by Frank's decision to drop him from the Champions League squad for the second time this season and is keen on a loan move to Paris FC in search of more regular football and a chance to fight his way into France's World Cup squad.
The Spurs boss is under serious pressure, however, clinging to his job despite a mounting injury crisis and last night issued a call for UEFA to 'modernise' their squad rules to avoid the problems he faced with Tel.
'It's fair to say we have not many players,' said Frank ahead of Saturday's Premier League game at Burnley.
'The players we have we need to keep. In the Dortmund game with not many available players, it's difficult to change the game when you need it or keep the freshness up.'
Spurs finished Tuesday's win against Dortmund with 17-year-old defender Junai Byfield on for a debut and right back Pedro Porro in midfield alongside 19-year Archie Gray.
Injuries have prompted a swoop for left back Andy Robertson from Liverpool, but Frank wants Tel to stay because Richarlison is injured and Randal Kolo Muani, on loan from Paris Saint-Germain, has made little impact.
'It's very tough for Mathys,' said Frank. 'My challenge was that it could only be him or Dom. I couldn't sub another player out. If so, I would have done it.
'It's not nice but it's a football decision. It's not the same as saying I don't like Mathys at all. I chose Dom because of his experience. Luckily, he did very well.
'Unfortunately, it impacts on others. Mathys in this case, and we need to get around him. He was disappointed, that's natural. But he's been very professional. He's a strong character.
'He has done well for us in many ways and started four of the last five, that's a clear signal I trust him and believe he can do something good.'
Tel, 20, was omitted from the Champions League squad in September because Spurs only fill one of their four 'club trained player' quota so must operate in Europe with a 22-man senior squad not 25.
In December, they exercised a new UEFA clause to make one change to cover a long-term injury and Tel came in to replace Dominic Solanke against Slavia Prague.
Ahead of Dortmund this week though, the clause dictated that Frank had to decide whether to stick with Tel or bring back Solanke – and he opted for the latter.
'UEFA need to modernise those rules,' said the Spurs boss. 'When they made the rules, we had six group games, now we have eight. Before, there were no games in January. With the new format, almost every club needs to fight until the end.
'We are up from three to five substitutions. The matches keep creeping up. For the Euros and the World Cup we have bigger squads so we need to look into it.
'I don't know who's looking at it for UEFA, but we should try to do that. It's a big issue for player health.'
Clubs can make three changes to their UEFA squads after the league phase. 'I can't see why that shouldn't be more,' said Frank, who will have more difficult decisions looming after Wednesday's game at Eintracht Frankfurt.