Djustice Sears-Duru and Brian Alainu'uese will make their first PRO12 starts against Scarlets in Llanelli while Melrose prop Jamie Bhatti could make his debut off the bench.
Robert Harley, Peter Horne, Tim Swinson and Mark Bennett have been released from the Scotland squad and will play in Wales, but ten players have been rested ahead of next weekend's Test against Australia.
Speaking in the Evening Times, Gregor said: "We have both had challenges from our training, with us from Scotland and other countries the players represent, and with Scarlets it's Wales. We are both used to it.
"From a coach's point of view, it's more about making sure we get the leaning and organisation but we don't over-train.
"The Scotland players who came back have trained Monday, Tuesday and Wednesday so we had two much lighter days on Thursday and Friday and I believe energy levels will be really high for the game.
"For players who didn't go away to international camps, it's a big opportunity for those who have been selected. We have seen in the past, players have really grabbed that opportunity."
With more than 30 internationals on the books, the head coach is well-used to the challenge during the November Tests and Six Nations.
"It shows the true depth of the club," he said. "It's a brilliant feeling for a coach when you see a player working hard and finally gets his opportunity and he goes there and grabs it.
"These points are vital as well, it's a chance to keep ticking over and keep in that top four in a period when we will have a number of players away.
"The November Tests are slightly different than the Six Nations, tougher in some respects because we lose a Tongan player, a Canadian and a Fijian for our next game. They are available this week. But also there is a break of two weeks.
"If we can get a good performance and result in Wales, it sets up for a good run after November."
The future Scotland head coach added: "I think our players deal with the changes much better. We announced our team to the players two days before the game, normally we do that four days out. So they have trained well.
"Our international players have done really well: Peter Horne having trained Monday, Tuesday and Wednesday with Scotland, spoke about the plays we are going to do for five minutes without any notes, so that shows he has been doing the preparation.
"We have guys like Sila Puafisi who has been training in Madrid with Tonga and came back and trained really well on Thursday. It shows they want to train for the club and they prepare well."