Passing comma separated list to a stored procedure

I have a stored procedure that takes a list of values as an input argument. The list is in the format:

'DFG','ABC','ASD','FGH'

I want the result to be

SELECT field1, field2, field3 FROM Table1
WHERE UPPER(RIGHT(RTRIM(field1),3)) IN ('DFG','ABC','ASD','FGH')

here is my stored procedure. What am I doing wrong here?

CREATE PROCEDURE dbo.sp1
@list as varchar(200)
 AS

SELECT field1, field2, field3 FROM Table1
WHERE UPPER(RIGHT(RTRIM(field1),3)) IN ( ' ' + @list + ' ' )