A training ground issue resulted in the Swiss missing the 1-0 Tayside derby victory at McDiarmid Park, with former Motherwell goalkeeper Trevor Carson coming in to make an assured debut.
Ahead of the home game against Hearts on Saturday, Courts provided an update on Siegrist, saying: "He has been scanned and we expect probably a definitive diagnosis in the next 24 hours.
"We have always been cautiously optimistic because the swelling was starting to go down pretty quickly, the pain and discomfort was starting to ease so he is feeling quite positive right now but again it is just a cautious optimism.
"We didn't want to sensationalise things when it happened, equally we don't want to be too optimistic so we only have to wait 24 hours to find out the extent of the injury."
Courts says he would have contested Peter Pawlett's second yellow card against St Johnstone for diving had the match-winner not picked up an Achilles injury which rules him out for the visit of the Jambos.
Pawlett was booked for celebrating his goal with some of the travelling United fans and was then ruled to have dived under the attention of Saints midfielder Murray Davidson.
Courts said: "I think it was quite clear there was a touch that forced him over.
"Pete is not a diver, or simulation or anything like that so we would have contested it but because he is going to miss this game, we decided not to."