The 19-year-old is yet to make a first-team appearance, but signed a contract with the Terriers in October which will keep him at the club until 2020.
The England Under-20 international has signed a deal to stay at Meadow Lane until the end of the season.
"He's a big, imposing keeper who talks really well and has a mature head on his shoulders," said boss Neal Ardley.
"We've done a lot of due diligence on the lad and we feel we're getting someone who if we didn't take on his first league loan we'd never be able to get to this club again.
"Ryan's got all the attributes and his coach puts him right up there with some of the top keepers he's worked with."