It will be a second loan spell at Huish Park for the Swansea-born 21-year-old, who spent a four-match stint with the Glovers last season, scoring twice.
MacDonald told the official Yeovil website: "I enjoyed my time (at Yeovil) last season. It's another chance for me to get some games under my belt. If I can chip in with a few goals along the way as well it will be a bonus."
MacDonald goes straight into contention for Saturday's home League One game against Brentford.