Do u think crutches would be helpful with patellar tendonitis?

Not good to use...: Generally, not a good idea because it will weaken the quadriceps muscle, which is the opposite of what you want. I would recommend the many physical therapy exercises which you can find online for strengthening the appropriate muscles.

Avoid crutches: If your injury is recent it may be reasonable to use for the first few days to allow the area to rest and avoid putting a load on a tendon. After first 5-7days it is usually unnecessary. Consider a patellar knee strap as well. See a sports specialist if it doesn't improve on its on or consider a virtual consult for more information. Hope that helps!