"I'm not at my strongest, I'm still working my way back to that because I had a couple of niggling injuries," Viduka told the Northern Echo.
"As you get older it gets tougher to shake off injuries and I'm into my 30s now. When you're young you recover quicker, you can shake things off and you can play with the knocks.
"It doesn't affect you as much, but I'm not that age any more. I just have to accept that and do the best I can."
While Viduka's form domestically has caught the eye, he could soon be ready to draw the curtain on his international playing days.
Of the opinion that at 32 his body can no longer cope with the demands of regular international football, Viduka is set for talks with Australia coach Pim Verbeek.
"It's a really tough decision for me with Australia because I'm at the age where I have to look after my body and get the most out of it that I can.
"I love meeting up with the guys and representing my country, but I want to play for Newcastle for as long as and as often as I can.
"I want to be able to give 100 per cent to Newcastle. I might be able to pick and choose international games, but I'm having a chat with the coach so we'll see what comes from that."