Iniesta has not played a full game for Spain since February 2009
Spain playmaker Andres Iniesta has a minor thigh injury, according to the national team's doctor.
The Barcelona player was taken off in the 39th minute of Spain's 6-0 victory over Poland on Tuesday.
"As he wasn't comfortable, we made the change - it's a minor muscle injury," said Dr Oscar Celada.
Iniesta, who missed much of the end of the La Liga season because of a thigh problem, helped set up Spain's first two goals in their World Cup warm-up.
He provided the pass for David Villa's opener in the 13th minute and started the move which led to David Silva's strike shortly afterwards.
Fernando Torres scored on his return from injury, while Cesc Fabregas and Xabi Alonso were also among the goals.
Spain coach Vicente Del Bosque said the attacking midfielder "came off as a precaution" after feeling the twinge in his leg.
The 26-year-old, who has not played a full 90 minutes for Spain since February 2009, is set to be examined again later on Wednesday.
"We will calmly carry out tests, but we can initially rule out any muscle tear. It's a minor injury, but we have to take precautions," Dr Celada added.
Injury aside, it was a vintage night for the European champions, with Alonso adding a third in the 51st minute before Fabregas scored with his first touch after coming on as substitute.
Torres replaced Villa midway through the second period for his first appearance since undergoing surgery on his right knee in April.
The Liverpool striker guided home Pedro's pass in the 76th minute before the Barcelona winger rounded off Spain's 11th straight victory five minutes later.
"The injury has passed and now I'm able to help my team-mates, so it's time to enjoy it," said Torres.
"Tomorrow (Wednesday) I'm sure there will be a lot of optimism and euphoria but we know it will be difficult."
Spain depart for South Africa on Thursday and will begin their campaign against Switzerland on 16 June before facing Honduras and Chile in Group H.