Wilkinson, who underwent surgery on his groin last month, has been included in an expanded list of nine replacements for the January 1 Guinness Premiership clash with Worcester.
But his training has been limited by Newcastle's heavy schedule and the adverse weather in the north-east and director of rugby Rob Andrew is not inclined to take any risks.
"We haven't made a decision on Jonny yet," Andrew said on Friday.
"We weren't able to train [on Friday morning] due to the snow, and we will have a run [on Friday afternoon] at Newcastle United's indoor complex, but we will give him a fitness test late on Sunday and see if he is ready to be on the bench.
"He will only be included if both he and ourselves are absolutely 100 per cent happy, and clearly we aren't going to force the issue if he's not ready."
Wilkinson, who has not played since November 11, admitted the groin injury had stemmed from his obsessive approach to practice and that he will have to tone down his routine.
"The reason this has happened is the shearing effect of the joints from the repetitive nature of the kicking," Wilkinson said earlier this month.
"I've put a lot of strain on myself without a doubt."
Andrew, who dismisses any assertion that Newcastle are to blame for Wilkinson's injury run, will sit down with the England fly-half and work out a new regime.
"We are looking at his training schedule, as we do with all the players," said Andrew.
"He has been extremely unlucky with the trauma injuries he has suffered in the last few years, but we are in an impact sport and there is no way of preventing these things.
"With this groin injury we need to sit down with him and talk about training, but we are doing that.
"As usual with Jonny there are many so-called experts in the press who think they know what's best for him.
"It just reminds me a little of the latter stages of the World Cup, when pundits were saying he's too intense, he just needs to relax, to have a few beers and go out with the lads.
"To say something like that about Jonny just shows that they don't know him at all, what type of person he is and what makes him tick.
"I think we know him better than anyone, and we will continue to manage him in the way we believe is best for both him and the club."