Watson and Nel made their comebacks from hand and calf problems on Saturday in Edinburgh's loss to Benetton.

Exeter Chiefs forward Sam Skinner, and Glasgow duo Grant Stewart and Stafford McDowall, have also been restored.

But full-back Stuart Hogg will not feature for Gregor Townsend's side as he recovers from a shoulder injury.

The British and Irish Lion suffered the damage in Scotland's second-round defeat by Ireland.

Townsend has also called up London Irish prop Gordon Reid, as well as Matt Fagerson and Byron McGuigan.

Glasgow back-row Fagerson and Sale Sharks back-three man McGuigan missed the initial squad selection through injury.

Fly-half Finn Russell played 65 minutes and scored nine points for Racing 92 in their rout La Rochelle, having missed Scotland's defeat by France with concussion.

Eight players have left the squad, with scrum-half George Horne, prop D'arcy Rae, hooker George Turner and centre Chris Dean dropping out due to injury.

Prop Alex Allan and forward Rob Harley have returned to Glasgow, back-row John Hardie is back with Newcastle Falcons while stand-off Duncan Weir has been released to Worcester Warriors.

Warren Gatland's Wales are chasing a Grand Slam after winning all three of their matches, while Scotland have a solitary victory from their trio of outings.

Watson, 27, has not featured at all in the championship after fracturing a hand in January, and his return to fitness is a major boost for Townsend.

Nel, 32, and 24-year-old Skinner were injured in the opening-round win over Italy and missed the losses to Ireland and Les Bleus.

Centre McDowall, 21, and Fagerson, a year younger, overcame ankle and shoulder injuries to score three of six Warriors tries in their thumping of Zebre.

Hooker Stewart, 24, came off the bench as Turner suffered a concussion in Parma.

Experienced loose-head Reid, 32, won the last of his 33 Scotland caps against South Africa in November, while 29-year-old McGuigan returned to action with Sale last month.