What kind of plant is it, and what type of medium is it currently potted in? Can you post a photo? Certain plants actually like to be 'pot bound - or what we think as pot bound. My African Violets for example love that snug, tight fit. If I potted them into a larger pot, they get shy and will stop blooming. Cacti can be like that too - certain types. My Christmas cactus is ginormous, but it's been in the same pot for over 5 years. I see no signs of stress and it blooms 2x/year.

Ha ha! I just noticed your other question.