The Dane left Samp last week for the Bees.
He posted to social media last night: "Hi Sampdoria!
"I want to thank all my teammates, all the people who work for the club. It was two years full of emotions, you have all been very close to me even in a complicated moment and I want to thank you from my heart.
"I will continue to follow you and support you. Thanks Genoa and above all to the great fans! Now a new chapter is about to begin but you will always be part of my path in my career."