Iniesta, 33, has admitted he needs to make a decision over his Barcelona future with his current contract up at the end of next season.
Herrera has been linked with a return to Spain with Barcelona and former Liverpool defender Nicol thinks he could be looked at as a potential successor in the midfield for Iniesta.
But the pundit does not think he is good enough just yet and reckons he would not get into the Barcelona team ahead of the current trio of Sergio Busquets, Ivan Rakitic or Iniesta.
"He's a key man for Jose Mourinho," Nicol ESPN FC.
"I'm not sure that he's a Busquets, Iniesta, or even a Rakitic. Rakitic hasn't been at his best but he doesn't have as much as those three have.
Barcelona line-up next season with Ander Herrera Thu, May 25, 2017
Click to reveal a possible Barcelona line-up for next season if they sign Ander Herrera
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GK: Marc-Andre ter Stegen
Steve Nicol thinks Barcelona could replace Andres Iniesta with Man Utd star Ander Herrera
It just depends, do Barcelona see Andres Iniesta playing for another full season? I would say not
Steve Nicol on Barcelona star Andres Iniesta
"It just depends, do they see Iniesta playing for another full season? I would say not which means you would need another body in there.
"The ones they have haven't done it, (Andre) Gomes particularly. Herrera, does he go? If he does I'm not sure he walks into the team."
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Former Tottenham and USA goalkeeper Kasey Keller agrees with Nicol that Herrera would get into Barcelona's starting XI and thinks he should stay in Manchester.
"You're starting, you're a key component of Manchester United," he said.
Kasey Keller reckons Ander Herrera should stay at Man Utd and not join Barcelona
"If they hadn't have qualified for the Champions League there might have been more of a case.
"I don't see him going anywhere unless Jose Mourinho doesn't see him in his plans.
"You expect Manchester United to make a ton of moves and if he's trying to fund certain moves in a direction that he wants and there's interest from Barcelona, then maybe it happens.
"But I don't think even Herrera looks at that Barcelona squad and think 'I'm a sure starter. I've got a pretty good thing going on here at Manchester United after it took a little while to get that going, why am I going to mess that up right now?'"