"At the moment, he (Sadiq Umar) is still a Roma player but it has been well documented that I am a fan, but it's just a case of watch this space", Gerrard told reporters on Saturday evening.
"He told me about the team; even though I already knew about Rangers and that they are the most successful team in the world. I know the team are in the Europa League and I know there is a big rivalry with Celtic".
Gerrard will be able to add Coulibaly to his Europa League squad, as they begin their qualifying campaign against Macedonian outfit, FK Shkupi on Thursday.
Speaking exclusively to RangersTV Sadiq said: "It is very good to be here, it has been good so far and I can't wait to start".
He smiled: "I don't like to say anything about myself but I am a hardworking player who always wants to help the team".
Coulibaly has made nine appearances for Mali.
They will become the eighth and ninth signings of Gerrard's tenure, following Scott Arfield, Allan McGregor, Jamie Murphy, Nikola Katic, Connor Goldson, Ovie Ejaria and Jon Flanagan in moving to Ibrox.
"I spoke to him when I was in Mali and he asked me if I wanted to join his team, and I said yes, although I was anxious it wasn't actually Gerrard [on the phone]!"
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