“It’s now looking as though I’m going to miss the Italy game,” said Ferris to BBC Sport.
Declan Kidney is already missing, for the trip to Rome, Andrew Trimble, Tommy Bowe, Shane Horgan,Jamie Heaslip, John Hayes,Rob Kearney and Geordan Murphy, and now Ferris looks to be out.
He added: “I basically aggravated an old injury in my left knee in last week’s game against Aironi.
“It was during a pushover scrum near the end of the game and I felt my knee go and a pile of bodies then ended up on top of me.
“It’s very disappointing but I’m hoping to be back for the second game against France.”