Scotland forwards Richie Gray and Gordon Reid have been ruled out of the rest of the Six Nations Championship through injury.
Glasgow Warriors second row Tim Swinson, who has already won nine caps, has been called up as a replacement on his 28th birthday.
Gray, the 25-year-old Castres lock, damaged an arm tendon during Sunday's 26-23 defeat by Wales at Murrayfield.
Warriors' Reid, 27, tore his medial knee ligament in the same game.
Fellow Glasgow prop Jon Welsh, who scored a late try as he earned his fourth cap against Wales, had already been ruled out of the remainder of the competition with a fractured hand.
Reid, who has been capped seven times, and British and Irish Lions lock Gray, who has played for his country 45 times, underwent scans at Spire Murrayfield Hospital.
While Scotland's medical team cannot say as yet how long Reid's rehabilitation will take, they estimate that Gray, who has returned to his club in France, "is expected to be unavailable for selection for the next three to four months".
Both will be missing for Scotland, who were also defeated in their opening game against France, for their remaining Six Nations fixtures against Italy, England and Ireland.
Fly-half Finn Russell could also be ruled out of at least the next game, at home to Italy on 28 February, after being cited for a tackle on Dan Biggar at Murrayfield on Sunday.
Swinson earns his recall after scoring a try in Warriors' 54-10 win over Zebre in Parma on Sunday, helping his club return to the top of the Pro12.
If selected, it would be his first appearance for his country since their summer tour, having withdrawn on the eve of Scotland's autumn Test match against New Zealand with a back strain.