Get Data From Half-Variable Table Name

Im really new to this and Im really bad.

but im trying to get the userID From a table,

but the table is named "Table"+the productID

ie Table23
or Table54

has 2 columns, UnitId and UserID


heres my code

CREATE Procedure UserDetail
(
@UnitId int,
@ProductID int,
@UserID int OUTPUT
)
AS

declare @TSQL varchar(1000)

SET @TSQL= 'SELECT @UnitId , @ProductID , @UserID ' +
'FROM Table'+CAST(@ProductID AS char(20))+
' WHERE UnitId=@UnitId '


execute(@TSQL)
GO



and i get this error

Exception Details: System.Data.SqlClient.SqlException: Must declare the variable '@UnitId'



anyhelp would be aprciated,. thanks so much