Barker is now set for a return to face his old club again in the Carling Cup tie on August 11th at Don Valley.
Meanwhile a strong Millers side took Mansfield to the cleaners in the first half of yesterday's behind closed doors friendly at Doncaster's Keepmoat Stadium.
They led 4-0 at the break thanks to new boys Tom Pope (2), Kevin Ellison and a goal from Ian Sharps before Mark Robins made sweeping changes in the second period.
However the squad did not include striker Mark Burchill, which fuels rumours that the Scot is set to return north of the border after an unhappy 2008/09 campaign.
The Millers play Walsall in their first public friendly on Saturday at DVS, 3pm. It's a tenner on the gate, £5 concessions.