Asked if he thinks Hulkenberg's move makes sense, Heidfeld told Speed Week: "When you're not going directly to one of the top teams, it is difficult to know whether you're making the right decision.
"Of course, in 2012 Sauber had the faster car, and they have excellent facilities at Hinwil. But they are now doing without designer James Key, who has gone to Toro Rosso.
"It's always difficult to judge if you've picked the right car, but I can understand Hulkenberg's decision.
"He has been able to assert himself against the established and - in my opinion - the slightly overrated Paul di Resta, and now with this change he will get even more attention.
"It can be difficult to have a brand new driver to formula one as your teammate, but Esteban Gutierrez in my view was quite convincing in GP2," Heidfeld added.