Bad news for Chelsea and their fans, but it is what it is, and injuries are a part of football which is inevitable most times. It is now the job of the manager to slightly change his plans for the new season, i think Sterling can play in that role for the meantime and Chelsea can start the season with him as a striker and see what happens. Chelsea are definitely going to try to buy another striker before the end of the transfer window, but they must start this season without an orthodox striker, which gives the manager more to think about.
Hope Nkunku will not become the next Pogba 
He had show outstanding performance in the friendly match, now Chelsea don't have a player to play as attacking midfielder. Chelsea will meet Liverpool in the first match Premier League, Liverpool should able to score many goals because there are many Chelsea's players are injured.