However, Posh manager Darren Ferguson was thankfully able to give a positive update on the supporter's condition later on.
Wednesday night's match was all-square at 2-2 when play was halted in the 88th minute and referee Paul Tierney eventually decided to take the players from the pitch while the fan received treatment.
After a delay of several minutes, the players returned and played out the rest of the contest in a very subdued atmosphere, amid huge concern about the well-being of the supporter.
Happily, Ferguson was able to report later on: "It looks like the gentleman is going to be OK, it looks like he's recovered.
"He had CPR (cardiopulmonary resuscitation) and the most important thing is the man's fine. When life's at stake, football is irrelevant."
The Scot added that he thought referee Tierney handled the situation well.
"At the time I thought 'just call it off now', but he probably did the right thing in getting us off and back on," said Ferguson.