Sir Alex Ferguson fears the emotion of Manchester United's visit to Liverpool on Sunday could have a negative effect on his players.
The game will be the first for Liverpool at Anfield since the damning findings on the Hillsborough tragedy were announced by an independent panel last week.
Liverpool intend to mark the match with a number of significant gestures, including the formation a mosaic across three sides of the stadium.
Ferguson has already appealed for calm from United fans in what is certain to be a tense atmosphere.
And having gone through something very similar four years ago, on the 50th anniversary of the Munich air disaster, the Red Devils boss accepts it may have a hidden impact.
Ferguson said: "It's a possibility, I don't deny that. Human nature can be that way. When we played Manchester City for the 50th anniversary of Munich the place was so flat in the dressing room before the game. I even felt it myself.
"We just couldn't perform and were glad to get it out the way. It was such an emotional day for us and it could be that way on Sunday."
Having twice appealed for United's supporters to behave themselves, Ferguson opted not to deliver another plea, believing it would be pointless under the circumstances.