Seymour, 28, has been on compassionate leave since being involved in a road traffic collision in Hessle in March.
"I wish to thank all the FC fans for their ongoing support," he told the club's official website.
"I have never experienced such passionate, supportive people and we are forever grateful. Our daughter Monroe Maria was born in Hull so this city will always hold a very special place in our hearts.
"I now focus 100% on getting well. Thank you for everything."
Seymour signed for Hull in 2011 after spending 10 years playing Rugby League in New Zealand and Australia.