Steve Clarke wants Scotland's Euro 2020 play-off final against Serbia next month to act as an incentive for all players in or out of the current squad
Scotland host Slovakia in a Nations League Group B game at Hampden Park on Sunday night, before taking on Czech Republic at the national stadium next Wednesday.
The Scots go into the Slovakia game on the back of a Euro 2020 play-off semi-final win over Israel on Thursday and November 12 in Serbia offers the chance to reach the finals of a major tournament for the first time since the 1998 World Cup finals in France.
Clarke said: "The group of players who are here now have the chance to make themselves almost undroppable. That is the first point on that one.
"Looking ahead to next month, all the players who are not in the squad this time have to do everything they can in their power to make sure they are fit and playing as well as they can to make my selection process as hard as possible.
"So there is an incentive for them as well.
"What we have achieved is straightforward. We have given ourselves a chance in a one-off game away to Serbia for a place at Euro 2020.
"Realistically, since last November, that has been the target and aim. We have managed to take the first step and there is one more to come."
Clarke saw his squad depleted before the Israel game with Stuart Armstrong, Kieran Tierney and Ryan Christie all leaving due to coronavirus reasons while Liam Palmer, Scott McKenna and Oliver Burke missed out out with various injuries.
The former Kilmarnock boss drafted in 29-year-old Hibernian right-back Paul McGinn – brother of Aston Villa's John – 33-year-old Aberdeen defender Andrew Considine and Dons midfielder Ross McCrorie, who played and scored in Scotland Under-21s' 2-0 win over Czech Republic at Tynecastle on Friday.
Slovakia have their own Covid-19 problems with winger Jaroslav Mihalik, who started Thursday's Euro play-off win over the Republic of Ireland, out after testing positive.
The Slovaks are already without defender Milan Skriniar through coronavirus issues.
Clarke said: "I have to freshen the team up a little bit but not so we lose track or focus on the good things that have happened in the last few games.
"We are six games unbeaten and we want to continue that unbeaten run and so if I have to make some changes I will do it but maybe not too many.
"Slovakia are a good team, good players and like ourselves missing one or two players who might have been starting for them and they also had 120 minutes the other night and a penalty shoot-out.
"Maybe they will make one or two changes, I believe they have just lost another player to Covid-19 so that is an on-going situation for every country which we have to deal with."
On his three uncapped call-ups, Clarke said: "Ross has done very well for Derek (McInnes) in Aberdeen in central midfield but he can also play at the back and he can play right-back, so he is good cover.
"Andy Considine is Mr Steady. He has had a great club career at Aberdeen, a one-club man.
"I think in my time at Kilmarnock we were involved in 10 games against Aberdeen so I got to see him up close and personal, a seven out of 10 every game he plays.
"Although he hasn't been involved in international level before he has the experience to handle the situation.
"Paul McGinn is obviously in a position (right-back) where we are a little bit light in numbers at the moment. He is probably having the best season of his career so far."