The Australian was asked if he was surprised at the levels Archie Gray was reaching, especially when playing out of position in central defense.
Gray put in a creditable display against Manchester United in a 4-3 Carabao Cup quarter-final win on Thursday.
Postecoglou stated: “I said last week that he has been outstanding. We have no choice as we have no other centre-backs. You put an 18-year-old kid there - I shouldn't say 18-year-old kid as he's a man in every sense of the word - and he's handled it brilliantly, both from a footballing perspective... If you do it for one game you can sort of get away with it where you put a young player out of position in one game but he's done it in multiple games now against some pretty decent opposition.
“Like I said, as an 18-year-old he's handled it so well and it's not like he's surrounded by experience. Obviously our goalkeeper is out, our two centre-backs are out, our left-back was out last night. Him and Radu handled it awfully well, awfully well. I keep saying you take out the goalkeeper, two centre-backs and a left-back from any team and I'm sure it will have an effect.
“The fact that our guys, and it's not just the way they're performing, they're still trying to play in the manner we want to play. We're not making allowances that we've got Archie at centre-back or Radu or Fraser in goal, we're still trying to play our football and it's a credit to them.”