The Argentina star has denied influencing the appointment of the former Newell's Old Boys boss as Tito Vilanova's replacement
The 44-year-old was confirmed as Tito Vilanova's replacement - who stepped down to continue his recovery from a cancer relapse - on Tuesday, after a successful stint in charge of Messi's childhood side Newell's Old Boys.
That has led to rumours the four-time Ballon d'Or winner had a strong influence in the club's latest appointment, something he was quick to dismiss after Barca were beaten 2-0 by Bayern in a pre-season friendly on Wednesday.
He said: "I don't have anything to do with the signing of Martino and I have nothing to explain. It's [Barca president Sandro] Rosell and the club's thing. At that time, I said that he looked like a good coach, but I have nothing to explain.
"I don't know him personally and have never seen him or Luis Enrique, who was also linked. He seems to be a good signing as he has demonstrated with Newell's and Paraguay that he is capable. Hopefully he'll do well here.
"After Tito's departure, we must begin again. It will be a hard season for us."
Martino also enjoyed success with Paraguay, guiding the nation to the quarter-finals of the 2010 World Cup - where they were beaten by Spain - and the final of the 2011 Copa America, only to be beaten 3-0 by Uruguay at the final hurdle.