Left-sided winger Bignall, who is also 18, has already enjoyed a steady start to life at Whaddon Road, making five appearances in total, although last weekend's disappointing 3-2 defeat at the hands of Hereford saw him leave the pitch early with an eye injury.
"Reading have agreed for him to come to us for another month and I'm very grateful to them for that," manager Martin Allen told the club's official website.
"He has shown on a couple of occasions that he has the pace to get in behind people. He's only young but he has that pace, he plays on the left side where we are a bit short of pace going forward so I'm really pleased to have him here for another month."
He added: "I am very grateful to Reading FC as we are not having to pay any wages for either player."