Real Madrid appear increasingly confident of signing Hazard for a world-record £100m after making the Belgian playmaker their top target.
And Spanish goal ace Costa also seems on his way after telling friends he is sick to the back teeth of the English weather.
Chelsea would not raise as much for Costa, 28, as Hazard.
But the champions-elect would have to spend around £200m to replace both players with similar quality.
Madrid are convinced Hazard wants to move to the Bernabeu despite having more than three years left on his £200,000-a-week contract.
Club president Florentino Perez has vowed to sign another Galactico this summer.
Hazard’s team-mates are concerned this will be his final season in the Premier League.
And even manager Antonio Conte accepts that he could be powerless to keep his star player at Stamford Bridge with Real prepared to offer £300,000 a week.
While Hazard is expected to quit for glory, self-styled hardman Costa wants out because England is not SUNNY enough.
As well as a £250,000-a-week pay packet, Tianjin can offer a steamy sub-tropical climate with summer temperatures of 40 plus degrees.
A source said: “Diego loves having barbecues. It is a major part of the social scene in places like Madrid where the weather is pretty much guaranteed.
“His house is not far from the Chelsea stadium and he doesn’t have a huge garden.