The 21-year-old, who had a spell at Brighton earlier in the season, could make his debut in the Robins' home game against Rochdale on Saturday.
Boss Mark Yates told the club website: "He is a talented young player who we have known for a number of years.
"He will certainly add something different to the squad and can contribute to the team in a big way."
Meanwhile, veteran striker Julian Alsop has signed another month-long contract extension.
The 36-year-old has been playing from month to month since the start of the season, but Yates said: "I would like to keep him until the end of the season.
"Since I've been here, Jules has been fantastic. He's a leader in the dressing room and a big part of the squad."
Source: BBC Sport