LINQ Help - Looks up items in IEnumerable from IEnumerable

// returns back an ienumerable of string containing each user
 var users = list.Where(x => x.Field.Equals("assigned_to")).GroupBy(y => y.Value).Select(z => z.Key);

// returns back an ienumerable of result for this hard coded user
var testUser = statList.Result.Where(x => x.GroupByFields.Any(y => y.Value.Equals("Test User")));

Instead of hardcoding "Test User" I need to look up all of the values returned in users from above.