If your system shut down or crashed mid-save then the file will be corrupted and cannot be fixed. Likewise if you game has been force closed for any reason there is a chance of save game corruption.
Added for Football Manager 2020 is an auto-backup save. Within your save game folder there should be a file called ‘last save overwrite backup.fm’. This save will be a copy of the save game you last saved over. Please try this save first and see if it loads.
If it doesn’t, the only other way to get the save back is to try and use Windows ‘Restore Previous Versions’ function. This will not always be on by default so may only work for some users.
To use this functionality, first go into your 'Documents' folder. Within there should be a Sports Interactive Folder. Go into the Football Manager 2020 folder.
Go into 'games' and right click on your save which no longer loads. In the menu that opens is an option called 'Restore Previous Versions', click that and see if it works. It'll first scan for a previous version then potentially give you the option to 'Restore'.
If this option isn't available to you, it may be worth searching the Internet for a file restoration program, which would enable you to roll back to a previous version of the save game file. We don't have a specific program we can recommend but some users have been able to do this.
To make sure you don't have an issue like this again, we'd very much recommend going into your in-game preferences when you load up FM and make sure your auto save is saving regularly, say weekly or fortnightly so you always have a recent back up in case of any problems. We would also suggest making sure your Anti-Virus Program is correctly configured for FM and Steam.