The Latics were plunged into a crisis earlier this week when David Miskelly dislocated his shoulder at Stoke on Wednesday evening.
New boss Mick Wadsworth approached Red Devils counterpart Sir Alex Ferguson about taking the California-born 20-year-old, who was only too happy to help the Second Division side out.
Rachubka said: "Tony Coton, the goalkeeping coach at Manchester United, just phoned me and asked if I fancied going to Oldham which I said yes to because it sounded a good move.
"It is very difficult at Man Utd at the moment because of the competition there. To progress in football it's important to play first team football and this gives me an opportunity to do that and hopefully I can help Oldham out.
"It will also prove to myself that I can play at a level like this which is important to me at the moment."
Rachubka has recently returned from a loan spell in Belgium, where he spent time with United's feeder club Royal Antwerp.
