10 Dec, 12:23
Ireland's John Lacey will referee his first ever RBS 6 Nations while Alain Rolland is also included in the Elite Panel in what is his last season.
Speaking in the aftermath of the Cardiff game, Ulster head coach Mark Anscombe said: "Johann, at this stage, I'd say is pretty doubtful. He won't be around next weekend and with Dan (Tuohy) going (into camp with Ireland), that hurts us a bit
"But Lewis (Stevenson) came on and did a good job and we're fortunate to have someone of his capabilities and experience. Now we've just got to find someone else to lock up with him next week."