Both sides named unchanged sides from the weekend as they went in search of their first win of the season.
Coventry earned a creditable draw at promotion favourites Norwich in the first of three games on their travels before they can christen their new Ricoh Arena when they host QPR on August 20.
Millwall, by contrast, have endured a miserable summer of upheaval in which they have lost two managers, two chairmen and 10 senior players before crashing to a 2-1 defeat at Leeds in their opening game.
The visitors started the brighter of the two sides and almost broke the deadlock after just three minutes when Gary McSheffrey linked up well with Stern John, but was judged offside by the narrowest of margins when through on goal.
Millwall responded well with Marvin Elliott grazing the outside of the post after Serioux's long throw caused panic in the Coventry box.
Just minutes later, following another missed opportunity by McSheffrey, Barry Hayles burst through the Coventry defence only to be brought down by Richard Duffy. The defender may well count himself lucky to only receive a caution for the foul.
Within just two minutes of the restart the home side were reduced to 10 men when Serioux, booked in the first half for a foul on the lively McSheffrey, received a second for kicking the ball away despite the protest from his team-mates.
Millwall boss Colin Lee responded by replacing Josh Simpson with the young Portuguese summer signing Carlos Fangueiro for his debut.
As is often the case the side reduced to 10 men looked the more likely to score and the home side could have done just that minutes later through Hayles.
The former Fulham striker linked up well with substitute Fangueiro but was denied by some superb last-ditch defending.
As the half went on Coventry fought their way back into the game and should have gone ahead midway through the second half through John.
Duffy supplied a curling far post cross from the right wing which met the head of John and only a superb point-blank save from Andy Marshall stopped the visitors going ahead and ensured a share of the points.