Fly-half Priestland and flanker Lydiate have been struggling with knee and ankle injuries respectively, while centre Roberts suffered knee damage while playing for Cardiff Blues.
"With Dan Lydiate and Rhys Priestland we are still waiting," Howley said. "In terms of their participation in training, it was very limited last week. Dan and Rhys probably did about two or three sessions but they were just limited to skills.
"The next 48 hours is pretty critical and we are waiting to see how they are. They have come in this morning and they are a little bit sore after the weekend's endeavours but we are obviously hopeful.
"Jamie participated a little bit more than Dan and Rhys but we are still uncertain. He has not played for a long time, I think it's around five or six weeks, so we are, once again, waiting to see how the next 48 hours goes."
Wales kick off their Six Nations campaign against Ireland in Dublin on Sunday.