The Rossoneri had to part company with striker Zlatan Ibrahimovic and defender Thiago Silva due to financial reasons, while a number of veterans including Clarence Seedorf and Gennaro Gattuso also left the club.
Merkel, who departed from San Siro at the end of last season after a six-month loan spell from Genoa, remains optimistic for the Italian giants.
"The side has been weakened when you consider that they have lost two fundamental players in Thiago Silva and Zlatan Ibrahimovic," the 20-year-old told Sky Sport Italia.
"However, they still remain a great club and they'll still be able to do well despite the absence of those two champions.
"I would have liked to stay at Milan, but I'm now at Genoa and I'm just thinking about giving my all to this shirt."
Genoa will begin their 2012-13 Serie A campaign with a home game against Cagliari on Sunday, August 26.