This news could hardly be worse for Everton given that the young defender has enjoyed a breakthrough campaign and has been for me, the Blues best player this season.
Branthwaite didn't have a great first half at Stamford Bridge, then again no one in a Toffees shirt did, and he went off early in the second half in a game that was already long gone.
Monday's result was a very sobering and concerning outcome and raised some very serious questions about this team as the games begin to run out.
And this weekend Everton face another massive potentially season-defining game when they host Nottingham Forest on Sunday at Goodison Park.
So, Sean Dyche has even more very difficult problems to solve than simply trying to overcome the potential blow back and collapse in morale from such a dreadful result.
The most immediate question is who is going to replace Branthwaite at the heart of the Blues defence, assuming he is not able to recover in time.
The options are not too good. Dyche has few decent alternatives basically either Ben Godfrey or Micheal Keane being his only obvious choices.
Godfrey has played regularly recently under Dyche most often at full-back and although he hasn't been particularly outstanding he didn't play terribly either.
Keane is a player who I do not have any confidence in unfortunately given his past history of making so many elemental and often unforced errors when he has played in the past.
For me then the best option is to look at a different tactical approach altogether and change the formation appropriately.
I would be considering reverting to a back three with Seamus Coleman (who has previously played in the centre of defence) and Godfrey lining up either side of James Tarkowski.
This is not an ideal defence perhaps but I think that after such an awful defensive performance on Monday evening a change is perhaps necessary anyway.
That would also allow the manager to push Vitalii Mykolenko (or Dwight McNeil) and Nathan Patterson further upfield to support a midfield that also struggled to get to grips with the opposition.
Regardless of what decision he ultimately makes, Dyche is under huge pressure and needs to find the right formula and balance for a match on Sunday that Everton have to win.