Djokovic has not played since losing in straight sets to Russian Daniil Medvedev at Flushing Meadows in September.
Inordinately long toilets breaks and medical timeouts at critical moments could soon be a thing of the past.
The Serbian fell short of making it a Golden Grand Slam as he failed to win the gold medal at the Tokyo Olympics.
Berrettini beat tournament favourite, Cameron Norrie, in the final as Humbert beat Andrey Rublev in Halle.
Stan Wawrinka has pulled out of Wimbledon with a foot injury that has also forced him to miss the ongoing French Open.
According to Serbian World No.1 Novak Djokovic, a shift in the favour ATP rankings seems "inevitable".
Rafael Nadal defeated Stefanos Tsitsipas 6-4, 6-7(6), 7-5 on Sunday to win the Barcelona Open for a record-extending 12th time.
Rafael Nadal becomes the first player in the Open Era to have won 450 matches on two different surfaces.