Baba Rahman (£14m)
Signed at the start of Mourinho’s final season in charge of his second stint, the Ghanaian played just nine games before the Portuguese was sacked in December 2015.
Rahman played 23 matches during his first campaign at Chelsea but, incredibly, he hasn’t made an appearance since then despite still being contracted to the London club. Injury and loan spells have meant he has rarely been seen on the training pitch at Cobham for the last four years.