Iniesta is a key component of Vicente del Bosque's squad and produced a sparklingly creative performance in Tuesday's 6-0 thumping of Poland in a friendly international before being forced off.
A scan the following day showed there was only slight swelling and no tear.
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"Andres is progressing very well with the minor muscular problem he sustained," chief doctor Oscar Luis Celada told television station Telecinco after Saturday's morning training session at Spain's base in Potchefstroom.
"We still don't know if he'll be fit for the Switzerland match but the feelings are positive," he added.
"There are still a few days before the World Cup starts for us and there is time to decide."
"Little by little I am doing more and the feeling is good," Iniesta said in an interview with TVE television.
"Let's see how things go the next few days and I hope I will have a chance to play."
If Iniesta is not ready for Spain's opening match against the Swiss, Del Bosque has a wealth of talent to replace him in the starting lineup, including David Silva, Pedro and Juan Mata.
"Andres is extremely important for us," Silva said at a news conference after Saturday's morning session.
"Thank goodness he is recovering and the sooner he is back the better. He is a great player and he gives us a lot of joy."
"Injuries are part of the world of soccer and all sports and sometimes you can't do anything about them," Arbeloa said at the same news conference.
"But we are 23 players and if someone gets injured we definitely have good alternatives to replace them," he added.
Xabi Alonso finished Saturday's morning training early as a precaution after suffering muscle tiredness.
