The full-back had to cut short his loan spell at Sheffield United last season after injuring his shoulder in February. The 20-year-old has battled back to full fitness and played in four of the Reserves' five games so far this season.
Riley told MUTV: “Obviously I had the setbacks but I guess they just set you up to come back. You want it more when you're sat on the sidelines, watching the team playing. You just want to play. I'm feeling good and I'm feeling strong.
"I'm happy to be back playing and happy to have the armband."