New Delhi, June 14 -- nobody endures 5 a.m. drug-testing knocks on their door just to play doubles.

Petkovic, the retired German player who now co-hosts the Becker Petkovic podcast alongside Boris Becker, was blunt about what she believes is the real logic behind Williams's return to professional tennis after nearly four years away. Williams, 44, has insisted throughout her comeback at the Queen's Club Championships that she has no plans for singles - that she is playing doubles because she missed the competition. Petkovic doesn't buy a word of it.

"In my opinion, no person in this world, no athlete in the world, voluntarily goes back into these anti-doping protocols, and especially not Serena Williams," Petkovic said on the podcast. "Y...