He asserted that the club is "in a much better place in all areas" than when he took over in the summer of 2023.
Spurs have dropped to 15th in the table following Sunday's defeat to Everton, winning just one of their last 10 league games.
Asked about why they are not performing on the pitch, Postecoglou said: "Just injuries.
"You can walk outside and say ‘Jeez, it’s really bright’ and look at the sun and think ‘maybe it’s not the sun.’ But it’s the sun, mate. We’ve just got injuries.
"You can do a million investigations and talk to anonymous sources but you don’t need to talk to anonymous sources you can talk to me.
"Every decision that is made is on me. I’m responsible for it. I’m the one that is guiding this. If you’re looking for a head on a stick take mine.
"But I am absolutely 100 percent confident that we are in a much better place in all areas of the club today than we were when I started.
"You can have 50 players but at the end of the day we have had a really bad set of circumstances with injuries," Postecoglou added.
"They have cascaded on us in terms of key areas of the park. Irrespective of the size of the squad or whatever the squad should be, any team would get affected by that. I get that people want to delve deeper into that but ultimately that’s the situation we are in.
"I don’t think anything could have changed any differently. Any team that loses the amount of players we have, irrespective of your squad, and to key players.
"We haven’t lost the 18-year-olds in our team, we have lost our starting goalkeeper, centre-backs, left-back, strikers, you name it we have lost it for all different circumstances. From that perspective it is not about the size of the squad I think it is about the cards we have been dealt with."