Small lump on wing

I have a male budgie with a small hard lump on his wing
It's slightly smaller than a garden pea and the tip is slightly yellowish in colour. It's very hard and firm.

He's still eating fine but he does appear to be grooming more vicarious than normal. I'm planning to take him to the vet this weekend (only time I could secure a ride there) but I just wanted to see if I could find any advice before that