Rotherham are unlikely to make any more signings before the end of the month, according to manager Steve Evans.
Derby captain Richard Keogh has agreed a new three-year contract with the Sky Bet Championship outfit.
Oldham have further bolstered their squad with the capture of Lee Barnard on loan from Southampton until the end of the season.
Barnard was previously on loan at League One side Bournemouth, where he scored four times in 15 games earlier this season.
The 28-year-old is Oldham's third capture of transfer deadline day, following Reading's teenage midfield player Jordan Obita and veteran striker Chris Iwelumo into the club.
The signings come as Paul Dickov bids to guide the 19th placed Latics away from the danger, sitting just one point above the relegation zone.