Gilroy and Marshall, as well as Ferris are two of 13 Ulster players in the Ireland squad and while they will be available this weekend, the majority will be absent when the autumn internationals kick into gear.
But Doak - who revealed Ferris is set for a run out against Edinburgh - believes Ulster have the strength in depth to continue their start to the season.
"We're obviously delighted that the guys have been picked and its credit to the guys who have put themselves in this position - they've deserved it," said Doak.
"But we need to make sure we continue our winning ways on Friday night with whatever squad we put out.
"It's vital to have them involved and it's great to have them in the squad, obviously Stevie hasn't played much rugby in a wee while and it's great to get have him back and hopefully he'll have a good run out.
"He has trained for the last couple of days and so we're confident he'll be taking to the paddock on Friday, and then after that it's just about his fitness.
"He's pretty robust and once he gets into games and the adrenalin gets going, hopefully that will get him going.
"It's a bit frustrating for him because he feels good and then for whatever reason it comes on again but hopefully he comes through the next couple of days and we can get him on the paddock on Friday."
63x46.png){kind=logo}