The Ivorian forward left Stamford Bridge after eight seasons with the club over the summer, and has joined up with former team-mate Nicolas Anelka at Chinese side Shanghai Shenhua.
The 34-year-old won every major trophy with the west Londoners and had an incredible pedigree of scoring in major finals, notching goals in the League Cup, FA Cup and Champions League showpieces.
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And United boss Ferguson says the loss of such a key player can only be a good thing for Chelsea’s domestic competitors.
"When you think of the season he's just had, I must say it is a big boost for us that Drogba is leaving Chelsea," the Scot told The People.
"He scored that fantastic goal in the final with two minutes to go and his goalscoring record in the big games, in big finals, is incredible.
"As far as I was concerned, he won the Champions League for Chelsea."
The Blues have moved to replace Drogba with younger additions to their attack including Belgian forward Eden Hazard, and have also been linked with a big-money move for Porto superstar Hulk.
But they will largely be dependent on £50 million Spain striker Fernando Torres to lead the line following his Golden Boot win at this summer’s European Championship in Poland and Ukraine.