Del Potro will play in the season-closing tournament after he moved into the quarter-finals of the Swiss indoor tournament, and following the news that Rafael Nadal has withdrawn from the season-ending showpiece due to a persistent knee injury.
The Argentine said he sympathised with Nadal.
"I'm sad for Rafa, he's really trying in his comeback," he said. "But it's not easy after such a long time away. I had the same feeling with my wrist.
"We miss Rafa a lot on the tour. He is one of the best players in history, he will come back strong.
"I'm sure it will be very soon. He will be ready to win a big event again, I know that he can play better than me when he makes his comeback, I wish all the best to him."
There are two berths for London still up for grabs, with players including Jo-Wilfried Tsonga, Janko Tipsarevic and Richard Gasquet among those in contention.
Novak Djokovic, Roger Federer, Andy Murray, David Ferrer and Tomas Berdych are already through.
Meanwhile, world number five Ferrer secured a place in the quarter-finals of ATP Valencia with a 6-4 6-2 victory over compatriot Albert Ramos.
Ferrer, top seed in his home town event, eased through to a meeting with another Spaniard, Nicolas Almagro, in the final eight as he saved five of six break points.
Sixth seed Almagro stormed through the deciding set to defeat Sam Querrey 6-4 6-7 6-0, boosting his own chances of making London.
Almagro, who ended the singles career of retiring friend and Spanish compatriot Juan Carlos Ferrero by beating the former world number one in the first round, broke unseeded American Querrey's serve three times in the final set.
The winner of the Almagro-Ferrer clash will face either seventh seed Marin Cilic, who has a slim chance of making it to London, or qualifier Ivan Dodig, both Croatians who were already through to the last eight of the indoor hard court event.
On the other side of the draw, defending champion Marcel Granollers, whose triumph last year was only his third career singles title, made it through to the quarter-finals when he came from a set down to beat Frenchman Gilles Simon 6-7 6-3 6-2.
Granollers will play Alexandr Dolgopolov after the Ukrainian saw off Gilles Muller of Luxembourg 6-4 6-4.
The winner will face either Austria's Juergen Melzer, who beat Xavier Malisse 7-5 6-2, or Malisse's Belgian compatriot David Goffin in the last four.
ATP Basel second round results
2-Juan Martin Del Potro (Argentina) beat Brian Baker (U.S.) 7-5 6-1
6-Mikhail Youzhny (Russia) beat Matthew Ebden (Australia) 6-3 6-1
Benoit Paire (France) beat Lukasz Kubot (Poland) 6-4 6-4
Paul-Henri Mathieu (France) beat Nikolay Davydenko (Russia) 6-3 6-7(2) 6-4
Kevin Anderson (South Africa) beat Marinko Matosevic (Australia) 6-3 6-7(5) 6-3
ATP Valencia second round results
1-David Ferrer (Spain) beat Albert Ramos (Spain) 6-4 6-2
6-Nicolas Almagro (Spain) beat Sam Querrey (U.S.) 6-4 6-7(4) 6-0
Alexandr Dolgopolov (Ukraine) beat Gilles Muller (Luxembourg) 6-4 6-4
Jurgen Melzer (Austria) beat Xavier Malisse (Belgium) 7-5 6-2
Marcel Granollers (Spain) beat Gilles Simon (France) 6-7(4) 6-3 6-2
- Sports & Recreation