Had a horse getting injured for six weeks. I obviously took him out of his next declaration and let him recover. However, 3 months later, with the horse having fully recovered and fitness and condition bars full up, I tried to enter him in a new race and got this message "Not possible. The horse is seriously injured". I've tried with other races since but I still get the same message even though the horse is perfectly fine.

Wonder if anyone has had this issue. Quite annoying, only option seems to wait for the next season to be able to enter the horse in a race.

I had a horse like that. I put him out to grass, he was fine next season.

As Andy said mate it just means you can't run the horse until the following year mate

i got this issue put him to grass and still a year later cant race it same message

In that case I would retire him from the game.