The fear that all Shrimpers had with such a small squad has been realised.
Sankofa will be unavailable for a minimum of six weeks and there is no confirmation that Sunderland loanee centre half Jean-Yves M'Voto will start, but the odds are if he can get out of bed Saturday morning he'll get a game!
Of the other defenders left standing two are left-backs and midfielders Anthony Grant or Jean-Francois Christophe may face the Pirates in the back four; Grant to allow Simon Francis to move to centre-half, or Christophe slotting right in next to skipper Adam Barrett.
Blues boss Steve Tilson told the official site: "Osei's injury is a huge blow for us because he had come in and done a good job and we're also short of numbers. I haven't made up my mind what to do for Saturday's game just yet. It's not ideal but we have to try and remain positive and do what we can."
The club are going to a number of lengths to get Osei fit again as soon as possible for an injury that was not affecting him too badly up to the Saints game. However, it could get worse!
Tilly explained: "They have decided against operating on Osei's knee for the time being. They have worked the fluid off the knee to try and get the swelling down. They will monitor it but if it doesn't work then he will need an operation and that will mean him being out for a number of months rather than weeks."
Loanee left-back George Friend's month long loan spell was down to end after the weekend's game with Bristol Rovers, but Tilly will be hoping he can extend the deal with parent club Wolves.
He continued: "It is important we keep George. It's certainly something I will be looking to do."