Fagerson is expected to return this weekend after missing the Champions Cup defeat to Leinster due to concussion protocols, while McKay is also in contention having overcome an ankle injury.
However, Sione Tuiputotu, Huw Jones and Jack Dempsey won't feature in Italy.
Speaking to Scotland Rugby News, Peter Murchie said: "Zander should be fine off the back of the concussion against Leicester. He's coming through the protocol, so he should be good.
"The others are getting closer, but they're not going to be [involved] this weekend.
"Sione's been back on the pitch. Demmo, we're still waiting on that one, but he's working hard on his rehab. They are getting closer, but not [for] this week. Josh McKay is back available so that’s really good."
Murchie also gave an update on Matt Fagerson who went off with an ankle injury against Leinster that head coach Franco Smith described as "significant".
After an initial assessment in hospital, Fagerson underwent a scan upon his return to Scotland.
"We're still waiting back for the scan," Murchie confirmed.
"So fingers crossed, it's maybe not the break that we thought it might be at the time, but we're still waiting for the scan to be specific on what the actual damage is there."