The 20-year-old defender, yet to make the first-team breakthrough at The Valley, will go straight into Greg Abbott's squad for this weekend's League One game at Bradford.
"It's an area where we need cover at the moment and he's a very good player who can come in and do that for us," Abbott told the club's official website.
"He's a big, strong player who can play a bit of football as well, so we're looking forward to working with him.
"He comes very highly-rated and he's another who is very keen and hungry to be involved. Hopefully this will be a good month for him and us."
Feely joined the Addicks in February 2011 from Irish side Bohemians.