The pair sat out Wednesday night's 1-0 friendly win at Gainsborough Trinity, but Knill said this was just as a precaution.
Midfielder Ryan, a summer signing from Accrington Stanley, has a groin problem while defender Nolan has an Achilles injury.
"There is nothing to worry about, it is just precautionary," Knill told the club's official website.
The duo join midfielder Michael O'Connor and defender Cliff Byrne on the club's injury list.
O'Connor's knee "flared up again" in training this week according to Knill, while captain Byrne will not be fit until September as he recovers from surgery on a back injury.
United's first-team will spend two days training in the Lake District, before Sunday's Lincolnshire Senior Cup tie at Lincoln City.