From Chelsea's point of view you would think that you don't want to keep someone who doesn't want to be there and you want to realize some funds. They purchased him for GBP26.4m in Feb 2015. His current market value should be lower than that - something like 20m pounds or EU23m.
If we REALLY want him long term, then we could close this deal for a loan fee of 4m + obligation to buy for 18m. Chelsea would not have to pay his salary but still are wearing a 7m amortization charge on his contract. However, by the time we pay the 18m for him, his book value drops to 14m after 2.5 years of amortization.
Now, if Juve has ZERO intention of having the obligation to buy clause, then you would want the loan fee to be in the region of 5-6m. If the option is for him to rot on the bench at Chelsea or play a vital role for Juve in the champions league, you have a better way to realize more value for him after the season ends.
I think in the end a deal will happen here.