The 21-year-old has been in sparkling form, scoring four times so far this season for the Hoops, and may play some part in Dortmund on 7 September.
McGregor steps up from Scotland’s Under-21 side managed by former Aberdeen and Celtic midfielder Billy Stark.
Stark said: "Andy Robertson has stepped up from the U21s and now Callum McGregor. Whilst it has not been the most successful of campaigns, the other part of it is players going through.
“Club form obviously has a big part to that and Callum has had a great start to the season with Celtic so it's no surprise.
"I know Gordon has always liked the intelligence and football ability that he's got, so it's great for him."
McGregor’s Celtic team-mate Craig Gordon has also been recalled to the international fold. The 31-year-old, who has featured three times for Celtic this season, made his last international appearance in a 3-0 win against the Faroe Islands in 2010.
Sheffield Wednesday striker Stevie May and Dundee United midfielder Stuart Armstrong have to make do with places in Stark’s U21 squad for their double header against Slovakia and Luxembourg.
Strachan revealed McGregor has been rewarded for hisd efforts over the last year, where he impressed on loan at Notts County before his promotion to the Celtic first-team in July.
"There was room in that area to bring people in and it's nice to bring a youngster in," Strachan said.
"I like to have people in who can eliminate people and go by them, and he has shown that.
"Not just this season, he has shown that last season at under-21 level and Notts County, which was great because he has done something about his career.
"He has got off his backside at Notts County. It's easy just to sit here. So I like that attitude - get me out to Notts County and I'll play and deal with reality football.
"He has come back and now he is playing with Celtic and scoring goals, and going by people."
Scotland squad in full:
C Gordon (Celtic), D Marshall (Cardiff), A McGregor (Hull), C Berra (Ipswich), C Forsyth (Derby) Gordon Greer (Brighton), Grant Hanley (Blackburn), Alan Hutton (Aston Villa), Russell Martin (Norwich), Andrew Robertson (Hull), Steven Whittaker (Norwich), Charlie Mulgrew (Celtic), Ikechi Anya (Watford), Barry Bannan (Crystal Palace), Craig Bryson (Derby), Chris Burke (Birmingham), Graham Dorrans (West Brom), Darren Fletcher (Manchester United), Shaun Maloney (Wigan), James McArthur (Wigan), Kevin McDonald (Wolves), Callum McGregor (Celtic), James Morrison (West Brom), Stephen Fletcher (Sunderland), Chris Martin (Derby), Steven Naismith (Everton).
You can watch Germany v Scotland on September 7 live on Sky Sports 5 HD