The 28-year-old, who plays for Toulouse, will not be involved this weekend when the competition gets underway and will instead work on his fitness in France.
It's hoped Gray will be fit to be in contention against France in game two for Scotland on February 11.
Assistant coach Mike Blair was cautious when pushed on when he might return, but said it would be "sooner rather than later".
He said: "Richie wasn't involved in the autumn or the summer tour so it's a situation we have been able to handle in the past. Obviously he is a quality player and a guy we're really keen to see back and how he fits in - but he also needs to get himself right.
"There's no point having him here if he's not 100 per cent. When will he be back? Sooner rather than later but we can't put an exact time on it right now."