Heh, heh, how arrogant of Federer!
Del Potro is the ONLY player other than Nadal who has ever beaten Federer in a Slam final and, other than Djokovic, the only player ever to beat him in his hometown tourney, Basel plus their incredible semi-final in the recent Olympics! So naturally he's going to say that Delpo will be the next Best Thing! You don't think the GOAT could ever lose a Slam to some no-mark journeyman, do you? Who do you think he is....Rafa Nadal??
Seriously, Del Potro's 2009 US Open run means he will always have the potential to repeat that performance and make it to the very top IF he can remain injury-free and iron out a few mental issues. But that's a pretty big IF, especially where his physical fitness is concerned. He's yet to prove whether he can ever repeat his 2009 US Open run or whether it was just a once-in-a-lifetime, lightning-in-a bottle-type performance.