Top seed Dominic Thiem was knocked out the Rio Open in the first round on Tuesday, going down 6-3, 6-3 to Laslo Djere.
Former world number one Novak Djokovic suffered a surprise second-round exit at the Barcelona Open when the Serb was beaten 6-2, 1-6, 6-3 by world number 140 Martin Klizan on Wednesday.
A dominant Rafael Nadal arrived at one career milestone on Thursday but the speed of the Spaniard's rampage through the early rounds of the French Open suggests his eyes are fixed firmly on another more significant one.
Former World No 1 Ana Ivanovic was upset 7-5, 6-4 by 42nd-ranked Karolina Pliskova of the Czech Republic in the second round of the US Open on Thursday.
Images from matches played on Day 4 of the Australian Open at Melbourne Park on Thursday
The FIFA 2022 World Cup will kick-off in Qatar on Sunday, November 20. Here is a list of the 26-man squads playing in the quadrennial global football extravaganza.