He has won one challenger match on clay.
Considering he has played most of his career in challengers in the US, that's reasonably understandable. Of course, he won't have many wins because he ain't playing on the stuff. While his record is fairly poor on the stuff, it's not like Duckworth's is outstanding, especially this season, I really thought he would be getting this WC after his performance at the Australian summer but he hasn't kicked on at all, pretty poor record at clay challenegrs himself this season. If he had a few more wins in the challengers then he would be given a shot but when you have no viable guy on form on the red dirt, you have to go with who has the best season overall and who is closest to the cutoff, that's Marinko. I would be evry surprised if TA picked anyone else, especially since Marinko ahs travelled back down here for Davis Cup.