The Robins have the option to keep Spence until the end of the season.
In the absence of captain Louis Carey, who has been filling in at right-back in recent games, Spence is set to start at Coventry on Saturday.
Carey, 34, fractured his skull in the home win against Scunthorpe on Saturday and is expected to be sidelined for at least six weeks.
Source: BBC Sport
Source: BBC Sport