Federer is aiming to become only the second man – following American Jimmy Connors – to reach the landmark.
“I won’t let this get in my head,” said the 37-year-old SWISs.
The winners meet in this season-ending tournament at 18:00’s final on Sunday.
“I am happy this is just another week in this way,” said Federer, who’s seeking to claim a record-extending seventh ATP Finals title.
“It did not seem like it, but that I managed to return and play decent Tennis.
“Personally I am still not thinking of this number 100.
“I won’t let it make me go crazy since it should be something I am excited about and not something that I need to feel extra pressure.
“As long as I think Novak is at the draw anyway, he is playing good again, it is not likely to be simple.”
Djokovic’understands what to expect’ at rematch of Wimbledon closing
Djokovic is viewed as the man to beat following a run which has seen him win 34 of his past 36 matches at the O2.
31, djokovic, earned his first Grand Slam title in more than two years by beating Anderson and will be the favorite to win the rematch in the O2.
“Kevin is enjoying some great Tennis, it is definitely his best time and he has continued doing this throughout this tournament,” explained Djokovic.
“He is playing well, serving well, very aggressive, so I understand what to anticipate.”
Murray and Soares eye first final
Britain’s Jamie Murray and partner Bruno Soares bid to get their first look from the ATP Finals showpiece whenever they start semi-finals day against Jack Sock and American group Mike Bryan at 12:00 GMT.
Soares and murray, who’ve dropped at each of the past two years in the previous four, won their group with a record of three victories.
“We’re pleased to be in the semi-finals, the very first goal at the beginning of the week is getting from this group, however you get it done,” said the 32-year-old Scot.
Brazilian Soares dropped alongside Austrian Alexander Peya in the 2013 semi-finals.
“It is about time that I went one step further,” said the 36-year-old Brazilian. “I guess that is the year to go a few more.”