The Hornets are said to be closing in on a deal for Mario Suarez and the midfielder was left out of Fiorentina's squad for their Serie A clash against Torino on Sunday.
Flores, who has already signed Nordin Amrabat from Malaga for £6million and Sunderland goalkeeper Costel Pantilimon , worked with Suarez during their respective spells at Atletico Madrid.
Suarez moved from the Spanish capital to Fiorentina last summer, but the 28-year-old has struggled to settle in Italy, making only five league starts.
"We are expecting to incorporate another player during the week," said Flores after his side's 2-1 victory against Newcastle in the Barclays Premier League on Saturday
"At the moment we're supporting all the players we have in the squad. Probably what is coming is one central midfielder."
Watford ended their four-match losing streak in the league after second-half goals from Odion Ighalo and Craig Cathcart
Newcastle defender Jamaal Lascelles pulled one back for the visitors with 15 minutes remaining, but Watford saw out the victory to move up to 10th in the table.
Spanish midfielder Jose Manuel Jurado featured more centrally as Flores adapted his formation following his side's dour run.
"We needed to do something different after four losses," Flores, whose Watford side have now beaten Newcastle three times this season, added.
"I needed to transmit a different message to the players in the meeting before the game. It was the third time we've played against Newcastle and they changed things in the other matches.
"So for us it was important to change the shape to 4-3-2-1. Playing with Jurado and Troy Deeney behind Ighalo is working well. We created problems for Newcastle."
Newcastle, who remain in the relegation zone, have scored only six goals on the road this season, and Steve McClaren's side spurned a number of good opportunities at Vicarage Road on Saturday.
In contrast Deeney teed up Ighalo for the opener before the latter played his part in assisting Cathcart for Watford's second of the game.
"It is about quality players at the end of the day and undoubtedly Watford are doing very well because they are always in football matches and they are always creating opportunities," said McClaren.
"They have only scored 26 or 27 goals this season and Ighalo and Deeney have got about 22 or 23 of them, so you can see why Watford are doing well, and you could see today why we are where we are."
Source: PA