Full-back Stuart Hogg is still unavailable due to a shoulder injury as the Scots prepare for a pride-salvaging mission against Grand Slam-chasing Wales at BT Murrayfield on Saturday.
Glasgow hooker Grant Stewart and centre Stafford McDowell have also been added to the squad.
Russell made a try-scoring, 65-minute return from concussion for his French club Racing 92 in their 50-14 win over La Rochelle at the weekend.
Tighthead Nel and flanker Watson featured for Edinburgh in their defeat in Treviso at the weekend, while lock Skinner has not played for Exeter since sustaining a head injury early in Scotland’s opening Six Nations win over Italy.
Glasgow back row Matt Fagerson and Sale wing Byron McGuigan – who missed out on the initial squad through injury – and London Irish prop Gordon Reid also come in.
Eight players have dropped out. Scrum-half George Horne (shoulder), prop D’arcy Rae (ankle), hooker George Turner (concussion) and centre Chris Dean (back) miss out through injury while prop Alex Allan, back-row forwards Rob Harley and John Hardie plus stand-off Duncan Weir have been allowed to return to their clubs.
Assistant coach Danny Wilson was adamant yesterday that a number of the returnees would be ready for the rigours of Test rugby come the weekend as Scotland look to make amends for a deeply disappointing performance in the 27-10 defeat by France in Paris.
“Take WP for example, it’s just been a few weeks with the calf issue and most players bounce back quickly from that,” said the forwards boss. “He hasn’t had a long time out of rugby. Hamish is a little bit longer but still probably a medium term injury. “It’s about us making the right decisions in selection based on terms of the right preparation but also in terms of positions where there is an injury list, we need to bring players back to give strength to the squad. “But we’ll also make sure they’re ready to play.”
Wilson said that the fact Watson’s injury was to his hand has meant he has been able to maintain general fitness and the openside looks certain to start on Saturday and bolster a back row that has been particularly ravaged by injury blows.
“Yes, it’s allowed him to be able to do a lot of what he would do in a normal training week,” said Wilson. “In terms of running and contact at the weekend. “What I saw at the weekend, he certainly wasn’t shying away from anything, he was putting his head and his hands into things as he normally would. “He’s in a good place to come back into this week’s training and we’ll see how he goes in that.
“I think we’ve had almost two full back rows unavailable to us so to get some bodies back would be great.”
On Russell, Wilson reported: “He’s in camp today and training and it’s all good – he’ll be working hard towards the weekend.”