Unless you are eating junk food everyday, you shouldn't worry. But, try to consume it much less and make sure you follow the guideline of your doctor.
It not recommended for you to get a hair transplant. Your donor area is very weak and there isn't enough grafts to cover your bald area.
Looking at the photo you have provided, around 4000 grafts can be extracted from your donor area. But, the area that needs to be implanted plays a big role in the results and density of the hair you will have after the hair transplant. If you provide photos of the area that you need to implant, it will be easier for us to tell you what exactly to expect.
Even though tennis is not a contact sport, you must not sweat a lot and during the first 30 days of your hair transplant
Over the next 6 months, you might see some more improvements as the hair transplant usually take 12 months to show full results.
