Exporting for unity from illustrator

Ok so i have almost finished my game. And the only problem i have is that PNG files are low quality when imported in unity. I have tried changing Texture type, Mapping, Compression. My designer even exported in 2048x2048, but nothing seems to work. Tomorrow he will export at 1024x1024, 1024x786, 1000x750 Color space is RGB, Alpha channel is true. Now i downloaded some backgrounds and sprites from web and they are perfect. Can anyone help me with this.