The Manchester United midfielder has been included in the squad for both games after spending nearly a year on the sidelines with a serious bowel condition.
"I feel ready to play both matches," the 28-year-old told reporters. "I feel fit, I feel strong and I feel ready for the games. It's great to be back.
"Hopefully I'm playing and I can do my part in getting a good result for Scotland."
The Scots will be looking for their first win of the qualifying campaign when they travel to Cardiff to face Wales on Friday.