Goalkeeper Ruddy, 23, told BBC Radio Norfolk: "An 80% Grant Holt would probably still score you 15 goals a season and that's a lot at this level.
"If he can get himself up to 100% sharpness in the next few weeks, then we could be looking at 20, 25 goals."
City's promotion from League One last season was spearheaded by their three-man attack, consisting of Holt, Chris Martin and Wes Hoolahan.
And Ruddy, the man who faces the trio every day in training, believes they can have a similar affect this year.
"Grant's a goal scorer, he's a threat anywhere around the box," he said.
It's things like that you might look back on at he end of the season and say 'yeah, that was turning point for myself or the team'
Norwich goalkeeper John Ruddy
"With him and Chrissy Martin and Wes Hoolahan chipping in as well, it's priceless."
The Canaries' number one is looking comfortable between the sticks after a shaky start that included a slip-up against Everton in pre-season and conceding three goals on his debut.
But a penalty save against Swansea a month ago, which spurred his side on to victory, could have sparked his season into life.
"I needed that," Ruddy explained.
"Obviously it was my mistake that gave the penalty away, if I hadn't of saved it I would have been crucified, but thankfully I did.
"It's things like that you might look back on a the end of the season and say 'yeah, that was the turning point for myself or the team'.
"That's how football is, next time that might not happen."
Source: BBC Sport
Source: BBC Sport