Michael Schumacher saw Sebastian Vettel win the title in each of his three comeback years © Getty Images Enlarge Related Links Drivers:

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Michael Schumacher says the spending power of Red Bull was one reason that Mercedes was unable to challenge for titles in his three years with the team.

Having returned to Formula One at the start of 2010 in the hope of adding to his seven world championships, Schumacher retired at the end of 2012 with only one podium to his name in the three seasons.

Each of those years saw Sebastian Vettel win the drivers' championship with Red Bull picking up the constructors' title and Schumacher admits that the funds and equipment that Red Bull has at its disposal reminds him of his Ferrari years when he went on to win five championships in a row.

"It's a factor," Schumacher is quoted by Auto Motor und Sport. "Over the years Red Bull built an infrastructure and has a budget giving them the possibility to respond to anything in the best possible way. It is nothing more or less than what we had at Ferrari."

Nico Rosberg gave Mercedes its only victory so far since its return to Formula One when he won last year's Chinese Grand Prix.