All you need to know ahead of Saturday's game
Whilst disappointed with Tuesday night's EFL Cup exit at the hands of Nottingham Forest, boss Chopper took great heart from the display of his much-changed starting XI and admitted that the performance of some players had given him 'real food for thought' ahead of the trip to the Proact Stadium.
Over 500 Lions fans will be heading north to back The Lions at Chesterfield knowing that a win for Harris' side could see the south Londoners leap-frog their opponents and move into the top six.
Millwall, sitting eighth in the League One table, are one of seven teams currently on seven points including fourth-placed Chesterfield, who boast a goal difference of +3.
Danny Wilson's Spireites have had an up and down start to the season with two wins, one draw and two defeats from their opening five matches.
Having kicked off the campaign with a 1-1 result at League One newcomers Oxford United, Chesterfield were dumped out of the EFL Cup at Rochdale (1-3) before recording back-to-back wins against Swindon (3-1) and Walsall (2-0).
However Wilson's charges slipped to a 2-1 loss at Shrewsbury Town last time out and will be glad to be back in action on home soil, where they have been beaten just once in their last seven games, a 3-0 defeat by Sheffield United back in April.
The Spireites have won both home games this season by a two-goal margin - and to score two or more on this occasion is a 13/8 chance with Sky Bet.
Shaun Williams is the man in form in front of goal for The Lions with two in the last two games, including Tuesday night's wonder strike against Nottingham Forest. You can get 16/1 for Shaun to score first or last, and 5/1 that he will score in the 90 minutes. Top scorer Steve Morison is 9/2 to score first whilst Chesterfield's Gboly Ariyibi, the subject of a transfer deadline day bid from Barnsley, is 16/1 in the same market. No goalscorer is an 11/1 chance with Sky Bet.