The attacking duo will be wearing new numbers in the 2014-15 season while Thibaut Courtois has been handed the No. 13, with Petr Cech keeping hold of the No.1 jersey.
The England international made the shirt his own during his 429 Premier League appearances at Stamford Bridge, during which time he scored 147 top-flight goals.
The jersey was so well associated with Lampard, widely regarded as the club's greatest ever player, that skipper John Terry had led calls for the shirt number to be retired after the 36-year-old left the club on a free transfer this summer.
But Brazilian playmaker Oscar will now have the honor of wearing the No. 8 shirt, giving up the No. 11 to allow Didier Drogba to reclaim it.
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"Didier is a Chelsea legend and a senior player. I am happy for him to take the 11 and for me to take the 8," Oscar told the club's official website. "Lamps is another legend at this club and I hope I will be as successful in the shirt as he was."
Eden Hazard will also be wearing a new number in the coming campaign, with the Belgium winger taking on the vacant No. 10 from the departed Juan Mata.
Elsewhere, Thibaut Courtois has been handed the No. 13 jersey, with Petr Cech holding onto the No. 1 despite increasing speculation regarding the Czech Republic international's future at the club.
New signing Cesc Fabregas will wear the No. 4 shirt vacated by David Luiz while Filipe Luis and Diego Costa have been given No. 3 and No. 19, respectively.
Young defenders Kurt Zouma and Nathan Ake have impressed in preseason, and as a result have been rewarded with the No. 5 and No. 6 jerseys, while Victor Moses takes No. 18 following Romelu Lukaku's departure to Everton.
CHELSEA FC SQUAD NUMBERS – 2014/2015
1. Cech, Petr
2. Ivanovic, Branislav
3. Luis, Filipe
4. Fabregas, Cesc
5. Zouma, Kurt
6. Ake, Nathan
9. Torres, Fernando
10. Hazard, Eden
11. Drogba, Didier
12. Mikel, John Obi
13. Courtois, Thibaut
14. Schurrle, Andre
16. Van Ginkel, Marco
17. Salah, Mohamed
18. Moses, Victor
19. Costa, Diego
21. Matic, Nemanja
23. Schwarzer, Mark
24. Cahill, Gary
26. Terry, John
28. Azpilicueta, Cesar
31. Christensen, Andreas