Announced last month, the beta version, which contains the majority of the game's new features, will be playable up until November 5, after which any progress will be transferable into the main game.
"We had an idea that this pre-order promotion was going to be popular, but nothing prepared us for the wave of enthusiasm that we were hit with when we announced it last month," explained Sports Interactive's Miles Jacobson.
"If you've already pre-ordered your copy, then you can start playing the Beta version right now - and if you haven't then there's still time, as this offer will stay good right up until the day of release," he added.
Football Manager 2013 will include more than 900 new or improved features. It will launch with two new modes, 'Football Manager Classic' and 'Challenge'.
'Football Manager Classic' is a simplified take on the core game, removing various advanced features and speeding up matches. It allows players to complete a season in less than ten hours.
Meanwhile, 'Challenge' mode - first seen in Football Manager Handheld 2012 for mobile devices - gives the player a short-term objective; for example, to avoid relegation with a team severely hampered by injuries or to maintain a side's unbeaten run until the end of the season.
Other enhancements include an improved 3D match engine, deeper media interactions, the addition of directors of football and a revamped loan system.
Many of the new features are spelled out in a series of video blogs hosted by Sports Interactive's Miles Jacobson.
> Digital Spy previews Football Manager 2013
Watch one of the Football Manager 2013 video blogs below: