The match between Federer and Thiem will have major implications on the battle for a top-four seeding at the French Open.
Federer is currently third in the rankings with Alexander Zverev fourth and Thiem fifth.
Being seeded fifth opens up the possibility of meeting Rafael Nadal or Novak Djokovic in the quarter-finals at Roland Garros and Thiem says he is keen to avoid that.
He said: “A top-four seeding would help for sure. You avoid the biggest names in the quarter-finals.
“It would be nice if it doesn’t happen all the way to the deep rounds. It is very hard and tough. But a top seeding is a good goal yeah.”
15:25: The winner of this match will play Novak Djokovic in the semis.
Djokovic got through without having to play a match after Marin Cilic withdrew after coming down with food poisoning.
15:00: Hello and welcome to LIVE coverage of Roger Federer’s quarter-final clash against Dominic Thiem at Madrid Open.