I thought it might have been a full transplant but toupee seems more likely.
Seagal is almost unrecognizable to his heyday 
It's hard to tell, no real up close pictures of it like Travolta, but if it is a transplant it is a bad one, brings way too much attention to his frontal hairline.
He also did gain like 150 pounds and has fake tan or real tan regularly, everything about him now days looks fake. No natural look to him anymore.