The 21-year-old recently enjoyed a successful loan spell at Gresty Road, scoring three goals in six appearances.
Boss Steve Davis, who saw the deal cut short by the Championship outfit three days early, was keen to bring Hitchcock back to the club, but the Millers have moved in and acquired his services on a month's loan.
Davis said: "I've spoken to him everyday since he left just to keep him involved.
"But he's gone to Rotherham, it's just what happens, that's the loan market, that's how it is.
"He has gone there, it's disappointing but there are other people we like."
To make matters worse, Hitchcock could make his Millers debut against the Alex at New York Stadium on Saturday.
- Sports & Recreation