Aberdeen boss Derek McInnes has welcomed the return of his Scotland Under-21 trio ahead of Saturday's return trip to Paisley.
Their absence compounded some major injury problems with Aberdeen being without nine players at the start of a six-day period in which they played three games.
Defeats to Rangers and St Mirren sandwiched a draw at Hamilton so McInnes is delighted to get the reinforcements following their Betfred Cup exit.
"They have all been back in the building this week," he said. "Ross had to go through his heart scan and his blood tests and they are all fine. None of them have felt any symptoms and Connor and Lewis tested negative throughout.
"It is great to have them all back and get them in amongst things.
"Lewis has been a huge player for me and if he needed another endorsement of how important a player he is to our team then I think the last couple of games has shown that.
"They are at different stages but it's good to get them back in.
"Hopefully these boys can show their frustration in the right way now. They have had to sit in the house and kick their heels but we have plenty of games coming up."
"Niall has felt his hip and groin a wee bit," McInnes said. "He has done some work today but we need to see how he reacts to that. There is a chance that McGinn might not travel."
McInnes expects big improvement following their late 2-1 defeat against Jim Goodwin's men.
"We have better numbers to choose from this week, I think physically we will be better, but it will count for nothing if we are not more ready than we were first half," he said.