The lock has undergone surgery and is expected to be out for six to eight weeks after sustaining ligament damage around his thumb during last weekend’s United Rugby Championship victory at home to the Sharks.
The injury will come as a big blow to the player who has made an impressive start to the season alongside Richie Gray in the Glasgow second row.
The news is also a major setback for Scotland who kick off their Autumn Nations Series against Tonga at BT Murrayfield on October 30. They then host Australia, South Africa and Japan in Edinburgh over the next three weekends.
The 20-times capped Cummings missed the final two matches of last season’s Six Nations due to a broken hand.
His place in the Glasgow side for Saturday’s URC match against the Lions at Scotstoun will be taken by Lewis Bean.
Danny Wilson, the Glasgow coach, said: “For Scott, for Glasgow and for Scotland it’s a blow that he’ll be out for a period of time. But that’s the game. It’s a short-term injury really, but long enough that it will have an impact.
“It’s unfortunate because I thought he was playing well, getting back to some really good form. He’s had surgery and starts the recovery process now so he’ll work hard to get himself back.”
Cummings’ absence is one of four changes to the starting XV from the side which defeat the Sharks 35-24 at home last weekend.
The impressive Sione Tuipulotu drops to the bench and is replaced at outside centre by Nick Grigg who is making his first competitive start of the season; Jamie Dobie is preferred to George Horne at scrum-half, with Horne named among the replacements, and Rory Darge returns to the side at openside after recovering from a knee injury, with Tom Gordon dropping out.
Ross Thompson is retained as starting stand-off after impressing in the win over the Sharks. Duncan Weir, who has recovered from a head knock sustained against Ulster in the URC opener in Belfast, is named as a substitute.
Glasgow Warriors (v Emirates Lions, United Rugby Championship, Saturday, 3.05pm, Scotstoun)
15 Cole Forbes; 14 Kyle Steyn, 13 Nick Grigg, 12 Sam Johnson, 11 Rufus McLean; 10 Ross Thompson, 9 Jamie Dobie; 1 Jamie Bhatti, 2 Fraser Brown, 3 Murray McCallum, 4 Lewis Bean, 5 Richie Gray, 6 Ryan Wilson, 7 Rory Darge, 8 Jack Dempsey.
Substitutes: 16 Johnny Matthews, 17 Brad Thyer, 18 Murphy Walker, 19 Rob Harley, 20 Matt Fagerson, 21 George Horne, 22 Duncan Weir, 23 Sione Tuipulotu.