Ange Postecoglou blamed a "very disruptive week" for Nottingham Forest's 3-0 defeat at Arsenal but vowed "it won't take long" for him to impose his style on the team.
The 60-year-old's first game in charge ended in a disappointing loss as the visitors were second-best throughout, conceding the opening goal on 32 minutes courtesy of a sublime MartÃn Zubimendi volley.
Viktor Gyökeres added a second just a minute after half-time before Zubimendi headed in a late third, leaving Postecoglou to reflect on a whirlwind week after replacing Nuno EspÃrito Santo as Forest's head coach.
"It is no secret it has been a very disruptive week for the players," Postecoglou said. "Seven days ago their world was totally different from what it is today and you've got to understand that, I certainly do.
"I can't fault the players endeavour and effort. I thought we hung in there, we never really had control of the game at any point but we worked really hard in the first half and there were small seeds towards the end of the first half of us maybe being able to cause them some problems but the second goal straight after half-time killed the game.
"You can't accept defeat and you've got to be disappointed by it but in the context of what the week has been like, I can't fault the players in terms of what they were trying to do."
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Forest face Swansea in the EFL Cup third round in midweek before a Premier League trip to Burnley and the start of their Europa League campaign at Real Betis and when asked how long it would take to mould the team in his own image, Postecoglou said: "It won't be months, it won't be weeks, it'll be Wednesday.
"I can't afford to waste time. This is not a project. This football club had a strong season last year, needs to be stronger this year and my job is to get us where I want us as quickly as possible.
"So by Wednesday night we will start seeing some real principles being embedded. It won't take long and I am not going to let it take long. I'll make sure we turn it around because we have got an unbelievable opportunity this year to make an impact and I'm not going to let that slip."