"He's very young but he has demonstrated he has more than enough quality," Iniesta, scorer of Spain's winning goal in last year's World Cup final, said.
"He is extremely talented considering how young he is and it is for this reason the coach has opted to call him up."
Thiago was named man of the match after helping Spain win the European U21 championship in Denmark in June, an audacious 45-yard free-kick catching the Switzerland goalkeeper off his line to seal a 2-0 final victory.
He went on to light up Barca's pre-season with goals against the likes of Bayern Munich and Manchester United, prompting debates over the need for the club to continue their multi-million-euro pursuit of Arsenal captain Fabregas.
The man Fabregas and Thiago are seen as natural successors to, 31-year-old Spain and Barca playmaker Xavi, has also been impressed.
"He has these sparks that will give us a lot this season," Xavi said recently. "He has endless talent."
Thiago was born near Bari in Italy and his father is former Brazil international Mazinho, who has a World Cup winners' medal from the 1994 World Cup finals in the United States.
He joined the Barca youth system aged 14 in 2005, made his first-team debut as an 18-year-old in 2009 and possesses the touch and vision that has become the hallmark of players groomed through the club's renowned academy.
After two more seasons with the B team, making occasional appearances with the senior side, Thiago was rewarded with a first-team contract for the start of the 2011-12 La Liga season, when the European champions extended his deal to 2015.
Barca coach Pep Guardiola has been keen to try and play down the euphoria surrounding the youngster.
"He's in one of these moments where every time he shoots the ball goes in, but softly, softly, softly," Guardiola said on the club's tour of the United States.
"All types of excess are bad. He is very young, has a lot of ability, but still has a lot of room for improvement."