The Wales international, who played for Argyle during the 2009/10 campaign, enjoyed a short spell with Newport before departing Rodney Parade earlier this summer.
And the 25-year-old is now training with the Pilgrims in a bid to earn a deal.
"I think Darcy will admit he's lost his way a little bit but he's got an opportunity now," Sheridan told BBC Sport.
"We'll work him hard and hopefully he'll impress us enough to earn himself a contract.
"It's a case of getting Darcy fit, I know he's got the ability at this level.
"It's just a case of having a look at him for the next two or three weeks, look at his fitness levels and take it from there.
"He's way behind at this moment in time, so we'll try and work him hard and get him back playing and then have a look at him."