The 31-year-old striker made his debut in 2003 and is currently the team’s all-time top scorer with 50 goals.
New boy Raphael Dwamena, Majeed Waris and Jordan Ayew have been tipped to succeed Gyan as Ghana’s reliable goal punchers.
“I have watched Gyan and I think he is a unique player. I know the system has changed but I think Gyan is irreplaceable” Addo told GHOne TV.
“I have watched Majeed Waris in Europe and I really like the way he plays. He is quick and I hope he will be free from injuries because we need such players in the team but honestly, I don’t think he can fill the gab if Gyan retires,” he added.
However, former Ghana captain Stephen Appiah, who played with Gyan for more than a decade, believes there are strikers who have the potential to step into his shoes.
“I believe Gyan is a great player but there are others who can replace him but I don’t want to call out names of players that can replace him,” Appiah said.
“Gyan came to the Black Stars in 2003 and we gave him the chance and confidence so I believe the only way to find his replacement is by giving the new players the chance and the support they need.
“Gyan is an excellent player, because scoring 50 goals for the national team is not easy but you know he can’t play forever. He is not at his peak now, even though he is still our top scorer and he is still scoring.”
He added: “It is very important that at this point we get someone who can succeed him so that we can count on that person anytime Gyan is not around.”
Gyan is expected to play a part in Ghana's friendly games against Mexico and USA on June 28 and July 1 respectively in the United States.