Ireland could be without outside centre Jared Payne for this week's Six Nations clash with England as he struggles with a hamstring injury.
Payne sat out training on Tuesday but the Irish are hopeful he can recover for Saturday, with Thursday his deadline to prove his fitness.
"Everyone trained fully today apart from Jared Payne," said Ireland's forwards coach Simon Easterby ahead of the showdown at Twickenham.
"He trained probably 85 to 90 percent yesterday and ran well, but today he's going to do some work with the physios and continue that, and we'll give him until Thursday to prove his fitness."
If Payne does not recover in time, it looks like being a battle between his Ulster team-mates, Stuart McCloskey and Luke Marshall, for the vacant midfield spot. Alternatively, head coach Joe Schmidt could opt for Munster's Keith Earls as he is now fit after a recent concussion.
"I think we've got a few combinations we could run with," added Easterby.
"Keith Earls has played there and Luke Marshall has done too.
"I think Robbie Henshaw has shown himself to be fairly adaptable, he's played at 15 this year for Connacht.
"He's well able to be adaptable, and that's what we have to be when we have a few injuries. We need to be adaptable.
"There is a difference defensively between 12 and 13 but we'd feel comfortable that whichever combination we go with that they would have had enough time to gel together.
"We're confident we'll be in a good place whatever the combinations that take the field.
"Jared Payne has been excellent in that role at 13 both in attack but especially defence, he's been very dominant in that area.
"He took an early bump against the French and dug in very well to stay on the pitch and he got us out of trouble a few times.
"We're keen to give Jared the opportunity to come through on Thursday but after that we'll make a decision on what combinations will best fit if Jared doesn't make it."