Razgatlioglu stunned the WSBK paddock earlier this year by announcing he will join BMW next season, leaving Yamaha with a serious headache to find a suitable replacement for the 2021 champion.
While Denning suggested earlier in the year that Yamaha would likely promote internally from satellite team GRT in the event it lost Razgatlioglu, this possibility now appears to be fading.
German outlet Speedweek reported earlier this month that Yamaha is eyeing the possibility of signing Rea, despite the fact the Ulsterman is theoretically under contract at Kawasaki until the end of 2024.
Rea himself is thought to be disillusioned with Kawasaki's current lack of competitiveness and publicly questioned his employer's strategy regarding its use of concession points at Imola.
While Denning says there is no rush to finalise Yamaha's 2024 line-up, he admits that the brand is likely to have to be "open minded" about the prospect of signing a rider from another manufacturer, or even someone who is not currently racing in WSBK, to replace Razgatlioglu.
"Toprak is super-difficult to replace: the level he is riding at, the level he understands the bike, and indeed the way in which the bike has been developed to match his riding style," Denning told Motorsport.com.
"But it’s no good just being interested in one rider, they have to be motivated to ride a Yamaha instead of another bike, or to come to this championship from another paddock. Both sides need to gel together."
Asked specifically about the possibility of signing Rea, Denning replied: "I’m not convinced it’s possible, and frankly speaking it’s not really on our radar."
For his part, Rea didn't explicitly rule out a move away from Kawasaki when addressing the rumours surrounding his future.
"At this time of the year, there’s always rumours and stories and I guess Toprak’s seat is the big one to be filled,” Rea told the official WSBK website.
“From my side, there’s nothing really to say on my future; I will sit down with my wife, kids and family to understand it. I’m sure everything is ongoing, but it’s all rumours right now.”
Besides Rea, Franco Morbidelli has also been linked with the seat vacated by Razgatlioglu as speculation gathers pace that the Italian is poised to lose his Yamaha MotoGP ride to Alex Rins.
However, Denning believes Morbidelli could have other options to stay in the grand prix paddock.
"For someone like Franky, who only three years ago was fighting for the world championship until the last race or so, it makes sense, at his age, that his ambition is to stay [in MotoGP]," he said. "I believe that is his first priority."
Denning also didn't dismiss the prospect of signing Scott Redding, who appears almost certain to lose his works BMW ride to Razgatlioglu but has been strongly linked to the marque's satellite Bonovo team.
Redding's option to extend his BMW contract expired on July 15 with no official news forthcoming on the Briton's future.
Denning said of the British rider: "Of course he’s an option because we need a rider and he finished in the top three of the championship [in 2020-21 while riding for Ducati].
"The only problem with Scott was the timing of his option with BMW was not necessarily aligned with our timing. But if we find for whatever reason he is still available, he is one to consider."
Yamaha has already confirmed that Razgatlioglu's current team-mate Andrea Locatelli will stay on for another season in 2024.
