PSG coach Laurent Blanc said midfielder Yohan Cabaye (groin), center half Marquinhos (hamstring), winger Lucas (groin), and right back Serge Aurier (thigh) will all miss the Chelsea game, at least, while key midfielder Blaise Matuidi has a sore knee, and is rated as doubtful.
''We've lost four players but above all two points,'' a despondent Blanc said. ''We have to pull ourselves together and get ready for Tuesday.''
Lyon can move four points clear of PSG and Marseille - which drew 2-2 on Friday - if it wins at Lorient on Sunday.
''It's a big blow for us but we have to cope with it. It's the first time I've ever experienced such an extraordinary scenario,'' Blanc said. ''When you make your first two changes in the first 45 minutes, it's hard to judge when to make the third.''
Although PSG defended poorly, there were at least mitigating circumstances, since it played the last 10 minutes with nine players.
''I've never seen anything like it. We were very unlucky,'' PSG striker Zlatan Ibrahimovic said. ''We'll see what happens on Tuesday.''
To add to the woes, Ibrahimovic will miss the trip to Monaco on March 1 due to suspension after taking his shirt off when celebrating his second-minute goal. Ezequiel Lavezzi made it 2-0 shortly before halftime, as PSG appeared to be set for a confidence-boosting win.
Instead, the problems are piling up for Blanc, who finds himself under increasing pressure - unlike his counterpart Jose Mourinho. Chelsea has had a full week to prepare for PSG since it was not involved in FA Cup action this weekend.
Poor composure under pressure once again proved to be PSG's undoing - like it was in defeats to minnows Bastia and Guingamp - as Emiliano Sala scored in the 89th minute, and strike partner Herve Bazile struck in the second minute of injury time.
Cabaye limped off after 15 minutes and Marquinhos was replaced at the start of the second half by David Luiz, who was supposed to be rested for the Chelsea game.
Aurier hurt himself in the 70th, attempting a pass, and was taken off on a stretcher, meaning PSG was down to 10 men because Blanc had already made his three substitutions.
Things had started so well for PSG, which had won seven of its eight previous matches in all competitions - and drew the other against Lyon.
Cabaye released Aurier down the right and his cross was finished powerfully by Ibrahimovic for his 11th league goal of the season.
Ibrahimovic and Lucas then set up Lavezzi, who scored with a low shot from the left.
Also, it was Lens 0, Evian 2; Lille 0, Nice 0; Nantes 0, Bastia 2; and Toulouse 2, Rennes 1.
Monaco's home game against Montpellier was postponed because of bad weather.
