Barker, club captain, suffered a dislocated kneecap and ruptured medial, posterior and anterior crucial ligaments during the 1-0 home victory over east midlands rivals Nottingham Forest in March.
The 30-year-old underwent an operation in April and was ruled out for the whole of the 2012/13 season.
His rehabilitation is going well and the Rams' head physio Neil Sullivan has been impressed with Barker's recovery, but he insists there is still a long way to go.
"It is a small step in the grand scheme of things, but it is a big boost for Shaun to be able to do more physical work on the vertical treadmill," Sullivan told the club's official website.
"It is a great way for him to do fitness work without worrying about the impact that is going through his knee."