The South African native will leave the Kingspan Stadium after signing a long-term deal with the Dragons.
Roberts - after impressing the Ulster management during a trial period - was handed a professional contact but he soon came on the Welsh radar and was capped by Wayne Pivac during the autumn internationals.
McFarland admitted it was inevitable that if Roberts wanted to pursue his international career, he would have to leave Ulster and play his club rugby at one of the four regions in the Principality.
“Brad wanted to represent Wales and I totally understand that if he wants to continue his ambitions he has to play in Wales,” said McFarland.
“For us, the emphasis is on guys who qualify for Ireland. We already have one Ireland hooker so we’re looking for guys coming through.
“Brad’s done a great job, starting with Rainey Old Boys and joining us when we had some injuries, and really grasping his opportunities, and throwing himself fully into the club. He’s an Ulster player for the rest of the season so I’m sure he’ll have a big part to play.
“We’ll be looking to put a fourth senior hooker in there. It’s too risky to go with three hookers, so we’ll be looking for somebody who is Irish qualified for that last spot.”
Roberts was named in Wales’ Six Nations squad and will be available for Ulster’s United Rugby Championship game on Friday night against the Scarlets. However, there was no good news on the injury front for McFarland.
“Hendy (Iain Henderson) won’t be playing this weekend, but he’s making a good recovery,” he confirmed.
“Obviously being named in the Ireland squad means that he should be able to take part at some point in the Six Nations.
“Stuart McCloskey and John Cooney are progressing but we won’t know whether they’ll be available; they’re unlikely to be available this week I would think but very possibly the following week.”
McFarland is looking forward to catching up with Dwayne Peel on Friday night. The former British Lions scrum-half left his role as Ulster attack coach at the end of last season to become head coach at the Scarlets.
“I’ll look forward to seeing ‘Peely’. We had three great years and I really enjoyed working with him.
“He was a great score for me when I arrived and was always very supportive. He has a real passion for the game and probably bigger than that, he has a real passion from where he came from and where he’s coaching now.
“That’s something I really recognise, that sort of attachment,” McFarland added.
“He’s a great attack coach, really good, so we’ll be expecting fireworks when they come over.”
McFarland feels the next few weeks will be crucial if Ulster are to mount a challenge in the URC.
“It’s a block of five games if you include the Six Nations before we travel to South Africa,” he said.
“Four of those games are at home and five out of 18 is near enough 30%, so that’s a big chunk of the season.
“It’s really important but I’m more interested in our performances. (If) the guys that are going out on the pitch play with the same sort of positivity and urgency that we demonstrated in Europe then the results will look after themselves.
“If we play close to the level we’re playing at we’ll be very tough to beat.”