Hammers defender Upson said: "He's having the best spell of his international career so far. I really feel the jersey is up for grabs.
"Robert is never going to have a better opportunity to establish himself as No1 and play in a World Cup, which would be a good reward for the amount of hours and time he spent with the squad without making many appearances or getting any recognition.
"Over the last year his form has been excellent. I have obviously been playing with him at that time at West Ham and I can't remember any kind of mistakes.
"He's hung in there. He spent a lot of hours with this squad without even being on the bench and mentally that is very demanding. It's down to him and his performances now, which is all you can ask for."