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.
The only opportunity 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 2018 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 turn on 'New File for Every Auto Save' option under the auto saves. We'd also suggest turning it on onto 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.
*If your save no longer appears within Football Manager but can be found via your documents folder, please read the FAQ entry related to loading files without the correct filepaths here - https://community.sigames.com/faq/football-manager-2018/136_technical-support/142_pc/cant-load-save-game-as-theres-no-fm-filepath-being-created-r595/
Edited by Neil Brock