Rowett now has more than two months to assess his squad before he is able to add to it through the permanent or loan transfer market.
But which of his old players might the 45-year-old fancy at Millwall? HITC Sport looks at three possibilities...
Ikechi Anya (Derby County)
Anya was only a semi-regular during Rowett's year-long stay at Derby, but prove an attractive option for his former boss, whose side aren't the Championship's most creative - they've averaged the seventh-fewest shots-per-game in the league this season - and are arguably lacking in left-back depth. Anya has scored or made better than a goal every four games at that level (34 in 128) despite having spent much of his second-tier career in the aforementioned role, but is currently out injured. The Scot should be back later this year - by which point regular first-team football should be high on his agenda.
Jacques Maghoma (Birmingham City)
Maghoma is unlikely to solve Millwall's left-back shortage, although he is a Championship-experienced creative player who's extremely well known to Rowett. The DR Congo winger has made more of his career appearances under the Millwall manager (116) than any other boss. His game time has reduced at Birmingham, however, having entered the final year of his contract.
Matej Vydra (Burnley)
Vydra recorded his most prolific ever Championship campaign whilst playing under Rowett at Derby, scoring 21 goals in 40 games. His subsequent £11 million move to Burnley has not quite gone to plan, however, having yielded just 20 appearances and two goals in more than a year. The Czech is currently on the periphery of Sean Dyche's team and could fancy a loan move in January. Millwall aren't exactly short of strikers, although nine of their 14 league goals they've scored this season have arrived courtesy of just two - Tom Bradshaw and Matt Smith. Neither Aiden O'Brien nor Jon Dadi Bodvarsson have opened their Championship accounts in 2019/20.
Have something to tell us about this article?