Marchisio left Juve with the Serie A season having kicked off.
“It was a very intense period, everything was done in a short time," Marchisio told Sky Italia.
“I always used my head though and tried to make the right decision, I wanted to find a new team to play more, so we made this decision with no regrets, because life goes on. There's still a big desire to keep winning.
“I'd already spoken with [Giorgio] Chiellini and [Andrea] Barzagli in the dressing room and their advice was very important.
“Now I'm thinking about the present, because Zenit want to get back to winning and that's everyone's objective.
“We want to go as far as we can in the Europa League and bring the league title back here to St Petersburg."