Strikers Kyogo Furuhashi, Giorgos Giakoumakis and Albian Ajeti were already missing along with winger Jota.
Ahead of the trip to Dingwall, Ange Postecoglou said: "Nothing has really changed in terms of guys coming back. James, we are still assessing him and he will be out tomorrow night. We'll get some information in the next couple of days on him.
"Mikey Johnston, we are not sure about either because he pulled up a bit sore after the game. As I said he wasn't 100 per cent, but we will see how he goes for tomorrow night."
Kyogo Furuhashi remains a doubt for the Premier Sports Cup final against Hibernian on Sunday, along with Forrest.
When asked about the Japan forward's chances of playing at Hampden, Postecoglou said: "Who knows, I am not sure. He is not far off, it's a day-to-day thing. If he is ready to go then we will play him, if he's not then we will look to the following game."
The centre-forward has been "improving" but the Celtic manager is wary of setbacks.
"Him and the medical team are working hard and we will see what happens," he added.