Monk has surprisingly been put in charge of the Swans' relegation fight after Michael Laudrup was sacked on Tuesday.
"The board have taken a massive gamble on Garry," Legg told the Daily Star.
"It's a brave and bold decision to appoint him but it's also a risk because it's a huge responsibility to put on his shoulders."
Legg added: "Every manager has their way of doing things.
"I didn't hear anyone complaining about Laudrup's training methods or the time he spends away when Swansea were winning the cup, finishing high in the league or beating Valencia.
"But it goes back to last summer when he and the chairman weren't speaking to each other over signings. That's when the relationship broke down.
"I'm surprised by the timing of this announcement just before the derby. I guess Garry is now in a no-lose situation because there is no expectation."