The 27-year-old, who has scored six goals in 18 games since joining Derby on a temporary basis last August, confirmed the news via his Instagram account on Friday morning.
The ups and downs or football ay?! Unfortunately I have torn my ACL and will be missing for the rest of the season and beyond. I had my op yesterday evening and everything went very well. Obviously I am devastated but I know I’ve got the right family, friends and girlfriend to get me through this and come out the other side stronger ❤️ I’d like to personally thank @dcfcofficial on how amazing they have treated me through this process. Everyone from the chairman, manager, backroom staff, players and especially the medical department have been fantastic with me and I will be forever grateful for the support they have given me and I know I’m in the right hands to get me back for playing as soon as possible I’m sure I’ll be back scoring tap ins very soon! But until then I will be working my nuts off to get back playing! Sam x
Although an obvious blow for Derby, the Rams do at least have plenty of cover in the form of Matej Vydra, David Nugent, Cameron Jerome and Andreas Weimann.
The injury will likely see Winnall - whose move saw Derby midfielder Jacob Butterfield head in the opposite direction on loan - return to Sheffield Wednesday while he recovers and scupper his chances of a permanent switch to Pride Park this summer.
The former Barnsley striker is one of several long-term injury victims at Hillsborough, and joins Owls front man Steven Fletcher in being ruled out until next season.
Winnall still has two years left to run on his contract at Wednesday, where he remains a fans favourite.