The 22-year-old's initial deal at the John Smith's Stadium was due to last one month.
However, Huddersfield have the option to recall Mullally at 24 hours' notice.
"Anthony needs to play minutes consistently and I am happy for him to be a part of the Bulls squad," Giants boss Paul Anderson is quoted as saying by Sky Sports News.
"We have the option to recall him but at the minute I can't guarantee him the game time here."
Mullally joined Huddersfield from Widnes Vikings in 2013.