Leinster's Rob Kearney was carried off with an ankle ligament injury against Clermont
Leinster will be without a trio of their key Irish internationals for Friday's clash with the Ospreys following their bruising 29-28 Heineken Cup defeat of Clermont Auvergne.
Fly-half Jonathan Sexton - who kicked seven from eight against the French giants sustained a broken jaw - while talisman Brian O'Driscoll picked up a knee injury and full-back Rob Kearney was carried.
All three have been omitted from the Ospreys' 27-man squad for the Magners clash at the RDS but more worryingly for Cheika is the prospect of them missing the Heineken semi-final with Toulouse.
Sexton - who took the Ireland No.10 shirt from Munster rival Ronan O'Gara during the RBS 6 Nations - is the biggest doubt and Cheika admits he faces an anxious few weeks.
He said: ""I would say it is probably going to be a few weeks. I would say it is fairly touch and go as to whether he plays in the semi or not.
"Our first concern is this week's match (versus Ospreys), but he is definitely out of that one.
"Rob is not as bad as we first thought. When you get carried off on a stretcher it isn't ideal, but, again, he will be touch and go and he is definitely out of this week's match.
"We are probably a little bit more hopeful on Brian now, of getting himself right in the next couple of weeks."
There was better news for Cheika after prop CJ van der Linde, who withdrew at halftime of the Clermont victory, was included in the squad as were Irish international backs Shane Horgan and Gordon D'Arcy despite missing training on Monday.
England Under-20s head coach Martin Haag was full of praise for his World Rugby Under-20 Championship-winning side after Harry Mallinder inspired them to a 45-21 win over their Irish counterparts and a third title in four years.