He said of the former Wallaby lock's condition: "It's too early to call. There is still a little doubt so we will have to wait and see if there is any reaction." Harrison trained successfully at Newforge yesterday.
Former Ireland prop Justin Fitzpatrick at Ulster's training base of Newforge. The 32-year-old has been ever-present on the loosehead side of the province's scrum so far this season, lining out three times. He has made 38 league appearances, but is yet to score a try.
Ulster's New Zealand-born centre Paul Steinmetz on the steps at Newforge. The 29-year-old, who has become one of the Ravenhill faithful's favourite players, earned his one and only All Blacks cap as a 77th-minute replacement for Mark Robinson against Wales in November 2002.
McCall will not finalise his team for the meeting with the Ospreys until tomorrow as six of the nine Ulster players who are currently training with the Ireland squad and who are available for selection for Friday will not be back in Belfast until tomorrow.
The former Irish international said: "We will have to assess what happens down in Dublin in terms of the content of their sessions and the intensity of them. Our players have a down day (on Wednesday) in preparation for Friday but the Irish players are training fully.
"We have to get them back to Belfast and see how each individual has reacted to the three days they have had and also deal with the selection dilemmas that we've got from the game last Friday.
"All those things are thrown into the pot which is why we are not naming the team until Thursday."
Steinmetz poses for a photo on an exercise machine at Newforge.
Reflecting back on Ulster's first defeat of 2006 - the 20-15 loss to the Gunners last week - McCall said: "We were disappointing. If we are slack in certain areas, as we were at Murrayfield, against very good teams in this league, then we will be losing more matches.
"But if you look at the league table, everybody has beaten each other. Nobody is unbeaten in the league and that is what you'd expect in such a competitive competition.
"At Murrayfield, we didn't play as well as we would have liked, but we could also have won that match and were within touching distance of winning it against what was a good Edinburgh side. We now have to put that game behind us. It's all about what happens this Friday," he added.
"Last Friday is over, we have looked at the video in detail with the players and they are ready to move on this week."
**All photos by William Cherry for Press Eye/Inpho Photography**