According to a report in the Sun, Warnock hopes to convince the Hornets to sell their long-serving forward and then talk him into helping the Welsh club fight for their lives in the Premier League in the upcoming season.
The Welsh newcomers are bracing themselves for a relegation dog fight this season with Warnock, 69, wanting to agree a fee for the 30-year-old striker in the next 24 hours but may face competition for him if a bidding war starts as the experienced forward is admired by others.
Deeney, has had a successful spell at the Hornets, scoring 105 goals in 309 league games since joining the club in 2010 from Walsall.
The Bluebirds are also refusing to admit defeat in their loan bid attempts for Liverpool's 22-year-old midfielder Marko Grujic.
Serie A club Lazio are rumoured to want the Serbia international, but Warnock is selling the idea of guaranteed game time with the highly-rated youngster.
Following the 2-1 defeat to Rotherham on Thursday last week, Warnock stated: "If not Marko, (we want) somebody like that.
“We're still optimistic and we should know within the next few days on that one. I’m constantly in touch with him (Grujic), still optimistic but we’ve also found a back-up as well, which we’re trying to hold onto for another few days, just in case.
“I’ll be disappointed if I don’t get Marko but it won’t be the end of the world."
Grujic has found it difficult since his move to Liverpool back in 2016 from Red Star Belgrade, making a total of eight appearances.
The midfielder made six appearances last season for Liverpool before being loaned out to Cardiff for the second half of the campaign.
After his move to South Wales, Grujic was given a starting spot and made 13 appearances for the Bluebirds, scoring once as he helped the club get promoted to the Premier League.