However, the prognosis on the De Bruyne's muscle injury suffered against Swansea is positive, with Pep Guardiola confirming that he should be back shortly after the international break.
There was also good news on Vincent Kompany’s condition with his manager expecting his muscle fatigue to ease and give him the opportunity to return in two to three weeks.
The Belgian duo are currently in Barcelona receiving treatment with “the best doctor in the world” according to their boss, Dr Ramon Cugat.
“Kevin is not a big injury - in two and a half or three weeks, maybe he will be ready,” Pep told journalists at Celtic Park.
“Dr Cugat is the best doctor in the world and with him we know we are so safe.”
This will be Guardiola’s first time in the away dugout at Celtic Park and he also admitted that he’s looking forward to sampling the famous atmosphere.
“It's my first time in Glasgow, playing against Celtic,” Pep said.
“Everyone talks to me about the atmosphere, I'm looking forward to playing here. I know how strong they are here.
I spoke with my old players, and they have said this is a special environment.
“We've started well and tomorrow we have a big opportunity to step forward. This group is so tough. I'm so happy with the performance against Gladbach but it is just one game.”
Pep also praised the work undertaken by Nick Cushing as MCWFC boss and all of his players and staff.
Man City Women won the FA WSL league title on Sunday afternoon courtesy of their 2-0 win over Chelsea Ladies.
The pair met at City Football Academy earlier on Tuesday and Guardiola believes that his team can learn a lot from Cushing’s charges.
He added: “It started three years ago and now they are champions. It was a compliment to meet the coach. Hopefully we can meet the girls and learn from them.”