4) Alexis Sanchez (Barcelona to Arsenal – £31.7m)
United fans may scoff at the Chilean’s inclusion on this list, considering how poor he was for the Red Devils, but we are focusing on his initial impact after signing for Arsenal.
Sanchez scored 25 goals during his first campaign for the Gunners, and he followed that up with 17 and 30 in his two subsequent campaigns. His drop-off, unfortunately, only came after leaving the Emirates.