Ferris suffered the injury in Ulster training on Tuesday
Stephen Ferris is in serious danger of missing Ireland's Tests against New Zealand and Australia next month after suffering a broken cheekbone.
Ferris sustained the injury in Ulster training on Tuesday and is expected to be ruled out for six to eight weeks.
An Ulster Rugby statement said that Ferris would require surgery.
Ireland will take on the All Blacks in New Plymouth on 12 June before facing the New Zealand Maoris on 18 June and Australia in Brisbane on 26 June.
The Lions flanker also looks certain to miss Ireland's warm-up game against the Barbarians at Thomond Park on 4 June.
More immediately, Ferris will be ruled out of Ulster's final Magners League game of the season against Connacht at Ravenhill on Friday evening.