City had dominated the contest for 70 minutes and powered into a 3-0 advantage thanks to an Erling Haaland brace and Ilkay Gundogan effort.
However, Feyenoord then reduced the arrears on 75 minutes and in a dramatic finale struck twice more in the last 10 minutes to draw level and claim an unlikely point.
Even then City could have won the game with Jack Grealish seeing an injury time shot strike the bar.
The result extended City’s winless run to six matches and reflecting on the result, the boss admitted it was a tough one to digest.
“[It’s] difficult to swallow right now,” Guardiola reflected.
“The game was good, we scored three and we could have scored more. At the end we are not stable enough to do it.
“We did a good game but then we were not able to control the last minutes.
“We have to accept it for many circumstances. The team was so committed in many things.
“It happened today. We are not able to win games.
“As a team we have always found a way to win games. Right now, after 3-0, other situations, it’s as if nothing happened. We could not score the fourth or fifth.
“Unfortunately something happened and we were not strong enough and we have to avoid the mistakes.
“Everybody knows the situations. We have to prepare and recover. Have a day off.
“It has been, is being and will be a tough season for us. We have to accept it for many circumstances. The team was so committed in many things.
“Unfortunately something happened and we were not strong enough and we have to try to avoid the mistakes.
The Feyenoord fightback came after City had made three second half substitutions with Gundogan, Nathan Ake and Phil Foden making way for Kevin De Bruyne, James McAtee and Jahmai Simpson-Pusey.
The boss revealed the factors behind the switches, saying he was anxious to avoid aggravating any more injuries to his depleted squad.
“Nathan come with injury. 3-0 with 20 minutes left I didn’t feel the game was in danger,” Pep added.
“Nathan has been injured many times and I didn’t want to expose him.
“Gundogan is the only holding midfielder we have. Foden has played a lot of minutes and Kevin needs the rhythm.
“Kevin, like Macca and Jahmai, is so stable emotionally. Rico was playing really good and Matheus had the best moment of the second half with a marvellous assist.
“We gave away the goal and it was not stable.”
