Here, we identify the key numbers around the Spain international's three years at Stamford Bridge.
28 - age
£32million - fee paid by Chelsea to Atletico Madrid in July 2014
120 - appearances for the Blues, 109 from the start
59 - goals for Chelsea
52 - Premier League goals in 89 appearances
20 - best goal return in the Premier League (in 2014-15 and 2016-17)
31 - yellow cards
1 - red card
12 - games missed through suspension
3 - Chelsea managers (Jose Mourinho, Guus Hiddink, Antonio Conte)
3 - major trophies won (Premier League 2014-15, 2016-17; League Cup 2014-15)
Source : PA
Source: PA