The Schalke defender was forced out on 39 minutes after attempting to thwart an effort, and was replaced by Anderlecht youngster Frank Acheampong.
Grant, according to reports from the Black Stars camp in Port Gentil, has tried Acheampong, Ebenezer Ofori and Edwin Gyimah at the vacant position during training sessions ahead of Mali clash on Saturday.
“I am still thinking about who will replace Baba Rahman," Grant told Supersport. "He is a wonderful player and it is sad that he got injured. We wish him a quick recovery.
"Everyone is not in happy since Baba is out because he is one of our best players. We will miss him as a player in the tournament and as a person," he added.
Baba is not the only player to bid goodbye to the 2017 Afcon, Egypt's goalkeeper Ahmed El Shenawy, Gabon's Mario Lemina, Burkina Faso midfielders Jonathan Pitroipa and Jonathan Zongo have all left the competition due to injuries.
Ghana top Group D with three points, while Mali and Egypt hold one each.