But a coach who is sometimes accused of not having a Plan B seemed relaxed about the alternatives.
The Whites failed in their appeal against Pascal Struijk's red card against Liverpool, compounding Diego Llorente' s muscle injury earlier in the game.
"Of the four centre-backs we have, we are not able to count on Diego, Pascal or (Robin) Koch but we're in conditions to resolve the issue," he said.
Koch has not played since the opening weekend of the season, out with a pelvic injury. No timescale has been put on his return. Struijk will be suspended for three matches after it was judged he had endangered Harvey Elliott in the tackle which inadvertently fractured and dislocated the Liverpool midfielder's ankle. Elliott is one of those who believes the red card was the wrong decision.
As someone who likes having a small squad, Bielsa prizes versatility highly and it will be used to solve the problem at St James's Park.
Luke Ayling is likely to be pressed into service in the centre of defence, with either Stuart Dallas or Jamie Shackleton used in his normal position at right-back. Mateusz Klich was an unused substitute against Liverpool.
So was Charlie Cresswell, a centre-back by trade but an 18-year-old whose only senior appearance came in the League Cup at the start of last season.
Bielsa dismissed rumours Patrick Bamford has a hamstring problem, and revealed Adam Forshaw is expected back in training next week after a muscle injury.