The 20-year-old American keeper kept a clean sheet on Wednesday as The Addicks's second string beat Watford 3-0.
Rachubka seemed set to move to Oldham in February, after making 16 league appearances for The Latics while on loan at Boundary Park.
However, after a fee was agreed between the two Lancashire outfits, Rachubka decided that he wanted to play at a higher level.
Being surplus to requirements at Old Trafford, Rachubka seems certain to move in the summer and Alan Curbishley may see his presence as strengthening the competition for Dean Kiely's number one shirt.
Sasa Ilic and Ben Roberts are currently the reserve custodians at SE7.
