The Blues beat a number of other high-profile European clubs to the services of the Palmeiras forward who will remain with his boyhood club for another 12 months.
Chelsea have invested heavily in young South American players since Todd Boehly and his Clearlake consortium took over from Roman Abramovich, but they hope Estevao will represent the jewel in their crown.
Gallas, however, believes his former club have paid way over the odds for a player who only has a limited number of senior appearances under his belt.
He told Lord Ping: ‘Estevao Willian only cost Chelsea £50 million because he’s Brazilian, your value is double for some reason!
’The issue with him might be that sometimes clubs think players can adapt straight away to a new league but it doesn’t work like that.
’There are too many obstacles like the language, lifestyle, even the weather. When you come to England it’s not easy so you have to think about that when signing new players.
‘Just because you pay so much money it doesn’t mean that they don’t need time to adapt.’
The days of signing readymade superstars appear to be over at Stamford Bridge, with the new-look recruitment team channeling their efforts into signing young, up and coming talent.
Gallas, however, believes Chelsea have missed an opportunity to rescue Neymar from Saudi Arabia after he signed for Al Hilal last year where he made just three appearances before succumbing to a serious injury.
Gallas added: ‘If I had the money I would’ve preferred to spend it on a player like Neymar. Someone with experience who will know how to adapt very quickly, it’s harder for young players.
’You can say that the money is an investment for the future but the Premier League is much tougher than La Liga, Ligue 1, Serie A and even the Bundesliga, it’s far more physical.
’It can be hard for players, even for Neymar. Because Neymar needs space and he also needs rest, playing every three games can be really intense.
’But it would be good to see him in the Premier League and fans will love him too, I’m not sure if he could work with Mikel Arteta at Arsenal but Neymar to Chelsea, why not?’
