The 26-year-old sustained a head injury playing for French club Racing 92 and missed the Scots’ third match of the tournament in Paris.
Scotland coach Gregor Townsend confirmed it was the other side of his face from the one that was badly injured two years ago and saw the stand-off wear a protective mask in a number of games for his former club Glasgow.
Russell returned swiftly for the home defeat by Wales and was superb in Scotland’s epic comeback at Twickenham.
“The concussion was okay but when I got it scanned, I realised I couldn’t play against France,” Russell told John Beattie on BBC Radio Scotland.
“When I got a knee to the head against Toulouse [in February], I fractured my cheek and that was what kept me out of the France game. The whole time my brain felt fine but I knew there was something else wrong.”
Russell also told the programme that there had been sporting socialising with the England players after the Scots retained the Calcutta Cup in London.
“We were chatting to them,” Russell said. “We were chatting to Ben Youngs, Owen Farrell, George Ford. Even [England coach] Eddie Jones, I had a chat with him.
“I’ve never really spoken to the English boys that much after the game.”