Even without Neymar and without Cavani in the second period, PSG held on to beat Bordeaux 1-0 on Saturday in France's top flight.
Coach Thomas Tuchel will be concerned whether Cavani, who clutched his right leg before going off, will be fit for Tuesday's trip to Old Trafford in the first leg of the last 16. "We have to have a great game".
'There is no good news this morning, ' Tuchel told Telefoot on Sunday.
'I am anxious, but only because we are missing key players.
"There are a lot of plans B. Without Ney, maybe without Marco, maybe without Edi".
The Brazilian will miss both legs of the tie against United due to a metatarsal injury in his right foot, the same problem that forced him to miss the second leg of PSG's defeat to Madrid a year ago.
"I do not know [if he will be fit]".
And Tuchel conceded the loss of Cavani, combined with the absence of Neymar, would force him to reevaluate his entire game plan for their biggest match of the season to date - the first leg of their Champions League tie with Manchester United.
Italian midfielder Marco Verratti is also doubtful due to injury.
"On Tuesday, a very important game is waiting for us", he said, per Goal. "They need to know how to control and handle the pressure, but without two or three of them, it is up to us to come up with solutions".
"It is super hard, and if we are missing several players, the challenge is even greater".
"If your key players are not there it's different". "But we're ready for Manchester and I have faith in my players".
Neymar is ruled out with a broken metatarsal and it looks as though PSG will be without their first choice striker Edinson Cavani too, after he was subbed off at half-time during Saturday's game against Bordeaux.
Mario Balotelli and Lucas Ocampos scored as Marseille won 2-1 at Dijon on Friday.