Ange Postecoglou savaged Timo Werner for his performance after hauling the Germany international off at half-time against Rangers.
Werner was replaced by Dejan Kulusevski who rescued a point for Tottenham with a late equaliser at Ibrox.
'He wasn't playing anywhere near the level he should,' said Postecoglou when asked if the change was tactical. 'When you've got 18-year-olds out there, it's not acceptable to me. I said that to Timo.
'He's a senior international, he's a German international. In the moment we're in right now, it's not like we've got many options.
'I need everyone to at least be going out there trying to give the best of themselves. His performance in the first half wasn't acceptable.'
Tottenham are locked in an injury crisis and patched-up at the back, missing three central defenders, their number one goalkeeper and two strikers.
'It's not really of great concern,' said Postecoglou, when asked how Werner had taken the criticism. 'We need everybody including him to be contributing. Because we don't have the depth to leave people out if they're performing poorly.
'We need them to play their part. Especially the senior guys. When I'm asking younger guys to do massive jobs. I expect a level of performance from some of the senior guys. And today wasn't that.'
Postecoglou's criticism of Werner came just 24 hours after he claimed he would not turn on one of his players in public when discussing Cristian Romero's comments on Tottenham chairman Daniel Levy.
Romero suggested after Spurs' 4-2 defeat by Chelsea on Sunday that the club were failing to compete for major trophies due to their lack of spending in the transfer market.
The Argentine defender told Telemundo Deportes: 'Manchester City competes every year, you see how Liverpool strengthens its squad, Chelsea strengthens their squad, doesn't do well, strengthens again, and now they're seeing results. Those are the things to imitate.
'You have to realise that something is going wrong, hopefully, they realise it.
'The last few years, it's always the same: first, the players, then the coaching staff changes, and it's always the same people responsible.
'Hopefully, they realise who the true responsible ones are, and we move forward because it's a beautiful club that, with the structure it has, could easily be competing for the title every year.'
Postecoglou responded by stating Romero was wrong to voice his opinion in public.
'A lot of what he said was good. Some of what he said wasn’t right,' Postecoglou said on Wednesday.
'It shouldn’t be done in public. I believe that with these things we deal with them within our own four walls because there are always issues that we need to deal with, the same way I wouldn’t publicly criticise a player or anyone else.'
But he refused to defend Werner's performance on Thursday night, despite Tottenham battling back to earn a draw after falling behind.
Overall, the Spurs boss was satisfied with a point.
'We were nowhere near our best,' said Postecoglou. 'Whether or not it's a fair result is for others to judge.
'But in the period of games we're grinding through, with a depleted squad, asking players to get up week in week out, it's a good outcome.
'In the context of where we are in Europe, with next games in the New Year, which gives us a chance to be in a better place, I think it's a pretty good point. We'll look back on this as an important point.'