The player failed a medical at Stoke City in January 2011 and they passed him over that month when he subsequently signed for West Ham who did not subject Ba to a medical.
In spite of those problems he never missed a training session through injury at Newcastle and has played 54 Premier League games for the club since he joined them in the summer of last year, scoring 29 goals.
The entire deal could potentially cost Chelsea more than £20m with around £15m in wages, at £80,000-a-week over four years, a further £7.5m to meet the buy-out clause, £2.5m of which is being divided between Ba and his representatives. The deal has been squabbled over by different parties claiming to represent the player who has negotiated through his friend Alex Gontran.
The departure of Ba has been a source of huge frustration to Newcastle manager Alan Pardew who suggested that the player had fallen under the influence of certain self-interested parties - "sharks" as he described them - in the last few weeks. Although Newcastle nominally signed him as a free agent in the summer of 2011, they also had to pay agents' fees.
"It's done. He will go to Chelsea with our blessing," Pardew said before kick-off against Everton. "He has done fantastic for us and it's not a bad thing, all the uncertainty is now done and we can move on.
"This club is bigger than any player for sure."
Once Chelsea have secured the deal for Ba, their attention will turn to bolstering their numbers in midfield with the Brazilian midfielder Taison from Metalist Kharkiv a possibility.
The deal to sell Daniel Sturridge went through yesterday bringing in £12m for Chelsea.
Although it is a good financial return, it leaves them short in attack with their big potential signing, the Colombian striker Radamel Falcao, expected to happen in the summer.