Ligue 1 champions PSG appeared on course to go top of the table thanks to first-half goals from Zlatan Ibrahimovic and Ezequiel Lavezzi at the Parc des Princes.
However, the capital club endured awful luck with Yohan Cabaye coming off early in the first half and centre-back Marquinhos being replaced at half-time.
The situation worsened when Serge Aurier and Lucas Moura both picked up injuries in the second half after all three substitutions had been made, and Caen's numerical advantage told as late goals from Emiliano Sala and Herve Bazile rescued a point for the visitors.
As well as the psychological blow of dropping late points, Blanc must also contend with a depleted squad ahead of Tuesday's last 16 first leg tie with the runaway Premier League leaders in Paris.
"I am not a doctor but it seems very complicated to recover for Tuesday," Blanc said.
"It is the first time that I have seen such a frantic scenario, it is still very rare to end a game in these circumstances.
"It started with the injury of Cabaye, followed by another at half-time and others again late in the game.
"In the end, we are left with four wounded, probably [out on] Tuesday."
Blanc was more hopeful that Blaise Matuidi would be okay to play despite a knee complaint, while stating Javier Pastore remains a risk with a calf injury.
