The 20-year-old Reading centre-back, who has started the Gulls' last three matches, has been challenged by manager Martin Ling to prove he is worth of a permanent deal with the League Two club.
"It's a four-month trial, in effect," Ling told the Western Morning News.
"In all the last three games, Gus has stood up to the demands of League Two football well, and he will be a valuable part of the squad between now and the end of the season.
"He has been with us once before and now he's got to prove that he deserves a longer contract next year."
Fellow centre-back Brian Saah returns from suspension for this weekend's trip to Burton.