The Swede held the F1 duties alongside an IndyCar seat with Arrow Schmidt Peterson Motorsport, scoring a podium finish in Detroit.
Ericsson is in talks to remain part of the Alfa Romeo team next year, but insists his primary focus is on his full-time race seat.
"I have a long relationship with Alfa Romeo and Sauber and I'm pretty sure I will have some part, but I have also said that I really want to focus 100 per cent on this Indy season," Ericsson told Expressen.
"The priority is not to be a reserve driver in Formula 1, the priority is Indycar. But I don't want to say too much about what it will be because it is complicated, with various different factors. We will see what Alfa Romeo and even what Ganassi wants."
At the Belgian Grand Prix earlier this year, Ericsson was brought over to potentially replace Kimi Raikkonen, who had picked up a minor injury during the summer break.
Ericsson skipped the IndyCar round at Portland for the call-up but was not put into the race seat at Alfa Romeo, when Raikkonen was deemed fit to compete.
"That's the problem with social media today," Ericsson said of the Spa situation. "Everything happened very quickly and Alfa Romeo chose not to say anything so it all came out in the wrong way."
Bahrain International Circuit - Winter testing