#4 Mateja Kežman
When Mourinho bought Kezman from PSV Eindhoven for a mere amount of £5.3m he was considered by many as the signing of the season. Before the season even started, he was even being labelled as the steal of the decade.
After all, the Serbian player had scored 105 goals in his 4 previous seasons making 111 appearances in the league playing for PSV. In his previous club, his partnership with Arjen Robben caused a havoc for the rest of the Eredivisie sides. By the end of the season, it became quite evident that it was Chelsea who had been robbed.
Even the presence of his Dutch counterpart Arjen Robben at Chelsea could not help him settle at the club. He could only score 4 goals in the entire league season out of which the first goal didn't come till December.
The only highlight of the Chelsea career of his was a tiebreaker at the 2005 league cup final against Liverpool which subsequently won Chelsea the title. He was shipped off to Atletico Madrid the very next season.