"He's had a few scans and he's been told there's no damage in there." Sheridan revealed to BBC Radio Cumbria.
"But it keeps swelling up and he needs to get to the reason as to why it is doing that and causing him pain."
Chadwick impressed for the Bluebirds after joining from financially-stricken Chester City in January, scoring seven goals in 19 appearances.
Sheridan added: "It's very frustrating for Nick at the moment. He's been given the go-ahead to play but he doesn't want to do any more damage by playing on it,
"He needs to find out what is causing it as soon as he can."
Source: BBC Sport
Source: BBC Sport