Roma have bolstered their ranks significantly with Ashley Cole, Juan Manuel Iturbe, Seydou Keita, Salih Ucan and Davide Astori among their new recruits.
"Roma can make life difficult to any team," Valero said. "They have made good quality signings and will battle for the Scudetto.
"We want to start the season in the best possible way but in order to beat Roma, we must play a perfect game."
Fiorentina coach Vincenzo Montella is set to hand Argentinian defender Jose Basanta and Australian midfielder Joshua Brillante their Serie A debuts against Roma.
The Viola finished fourth last season and will compete in the Europa League this term.
Roma fans hope the club's efforts in the transfer market this summer will help the team as they look to repeat last season's impressive campaign.
The Giallorossi finished runners-up to Juventus, losing just one league game at the Stadio Olimpico.
"We have been preparing for seven weeks and my team can't wait to play their first official game," Roma coach Rudi Garcia said. "The fact that we face a quality team like Fiorentina to start with is great.
"My job is to make sure my players maintain that hunger they had to win last season.
"We have had to strengthen our squad because we will play 22 games before Christmas and I must have at least two players in each position."
The Romans face a stern test on their return to the Champions League having been drawn in Group C alongside Bayern Munich, Manchester City and CSKA Moscow.
"It's going to be a very tough group," Roma captain Francesco Totti said. "Our rivals are very strong teams but it will be all the more fascinating to play against them."
Fiorentina will be without striker Giuseppe Rossi, who is out with a knee injury.
Juan Guillermo Cuadrado, reportedly a transfer target for Manchester United, will play in support of Mario Gomez in Fiorentina's attack.