Multiple Git Projects and one Visual Studio C# Solution

I have a setup in which I have two Git Repositories but one is dependant on the other and I want to build them using Team City. The first Git Project is a common layer (Common VS Solution) I use the projects in this solution across many other Visual Studio solutions at my company. This common Solution has 6 individual C# Projects. In the 2nd VS Solution (API Solution) I refer to some of the projects in the common Repository.  So my local directory on my machine looks something like this

C# Source Directory
Common Folder (Git Repo Common Associated with it and is a subfolder of C# Source Directory)

API Folder (Git Repo API Associated with it and is a subfolder of C# Source Directory)

In the API project I refer to some of the individual c# projects in the common folder. I'm curious on the best way to build this type of solution. Because right now when try to do a build for the solution in the API Folder TeamCity says it's missing projects that are in the common folder, which is true but I'm not sure how to download these projects and get the path correct.