Reports in the British media have indicated the Premier League club are on the verge of bringing the former Atletico Madrid midfielder to Vicarage Road.
A fee of £4million is said to have been agreed with the Serie A side as Watford look to add more quality to a team that has impressed on their return to the Premier League.
Speaking after his side's late FA Cup fourth-round 1-0 win over Nottingham Forest, Flores said: "There are little details [to be done] but Mario Suarez is very close to being in our squad.
"I think it is practically done. There are little details but I consider him a player of Watford.
"It [Suarez's signing] shows Watford are doing something really good because [Nordin] Amrabat, Mario Suarez and [Costel] Pantilimon want to come to Watford. So something has changed. I love that."
Spain international Suarez had previously worked with Flores when the Watford boss was coach at Atletico between 2009 and 2011.
Suarez made 121 La Liga appearances during his time at Vicente Calderon but has played only 13 times for Fiorentina since joining the Italian club in July last year.