How long after a hair-implant can I engage in Brazilian Jiu-Jitsu training?

Always check with your doctor for post operative care. If your doctor cleared you to go back to full physical activities then it should be fine.  I am sure you are well aware Jiu-Jitsu can sometimes be an extreme contact sport that may irritate your scar and recipient sites.  It comes down to using your judgement and following your doctor's recommendations. If you have concerns, ask your doctor.

Depending on where the grafts are placed and how many, since I use the automated FUE procedure I usually like to wait for six weeks for full contact sports. I'm not so much worried about you but a good strong kick to the head could really just rub several graphs and I think the risk benefit ratio of waiting six weeks far outweighs a little time off from training. Sorry.

Dear Peter,Congratulations in your procedure.The answer by your physician is partially accurate, depending on how the hair grafts were obtained. If you underwent a Neograft procedure, were the hairs are removed by drilling the hair from over your head, then the answer is yes, you can resume full activity.If your hair was removed by removing a strip of hair from the back of your neck, then you are at risk of having a thicker and more noticeable scar with your martial art.Ask to your doctor his thought related to your donor site. Also explained in detail the exercises that you will be doing. This might help him/her give you a better informed answer to your questions.Best of luck,