The 32-year-old striker hinted this week he could finish his career with the Magpies, which posed a couple of questions:
a) He only has one year left on his contract so perhaps he could retire, or
b) He hopes to sign a new deal.
But Kevin Keegan will not hold talks with the player until Viduka proves he can rid himself of the injury problems that have dogged his career for four years.
However, Viduka's return to training signals he could feature in some of the club's pre-season matches.
An injury to his Achilles tendon in May caused Viduka to finish the 2007-08 English Premier League season a few weeks early.
He had also been plagued by hamstring, calf and ankle injuries throughout last season.
Viduka: "It probably didn't go as well as I wanted in my first season, but sometimes things don't work out the way you want them to.
"Kevin Keegan is a very good manager to work for.
"He's so positive and very knowledgeable about the game.
"It's a pleasure to work with him and I'm looking forward to that for the new season.
"I've got this year left on my contract and then the option of another".