I would recommend putting truffle scent training on hold for the initial part of Blu’s recovery. You can resume working on the truffle scent when his mobility returns and during his rehab. The reason for this is so that he is not practicing this new great game while he is in pain or frustrated from inactivity. You will accomplish two things by putting the truffle scent on the shelf for the first phase of recovery. 1) you will prevent him from associating frustration with truffle hunting and 2) you will allow latent learning to occur.
That said, I would DEFINITELY continue doing scent work with him during his down time! It is a great way to keep his mind happy and if you do some work with a different odor (or even just finding food), you can help him cope with the inactivity. Work on targeting an object the same way you did for the target to sharpen his skills at telling you exactly where the object is. Or, teach him to find something that could be handy in the future, like the remote or your keys! You are simply playing the same game with a new object. He gets to do something he enjoys but you are using an object or odor that you don’t care about for future training. Does that make sense? Don’t worry. He won’t forget the truffle scent.
Pick some new tricks to teach him too 🙂
Then when you get the truffle scent out again, I suspect he will be jazzed to go. You can pick up training when he is allowed leashed activity and you can safely allow him to show his normal enthusiasm.