"I don't want anyone at this club saying it is a good time for us to be going to Manchester United because all that does is to motivate the other side," he told Sky Sports News.
"I know that they have some big players out and that maybe they have lost a bit of shine of late but I am not going to tempt fate.
"All I'll say is that we'll go there and be competitive and try to win the game.
"Don't forget that Manchester United are still the biggest club in the country, with the best players, the most money, the biggest stadium and the biggest crowds - so how can they be in a crisis?
"All we can do is try to win the match. We are among a cluster of clubs aiming for the top positions in the Premiership and every point you can pick up from difficult games like this does help.
"We had a tough game at Arsenal recently and now we have a tough game at Manchester United. Those clubs are still a little ahead of us even though we have closed the gap and Saturday's game will give us some indication of how big the difference remains.
"I respect Manchester United and what they have. It's not just about the Beckhams and the Keanes because they have a great squad of players."
Newcastle have failed to beat Manchester United at Old Trafford for over 30 years, although we can look back at a couple of FA Cup semi-final victories there.