A stunned Alex Corretja learned of Greg Rusedski's positive drugs test after stepping off court after training in Auckland yesterday.
He said it "sounds really strange" that the Canadian-born Englishman would risk his career in this way.
Corretja, the former world No 2 and a long-serving member and former presidentof the ATP's player council, added: "The first thing you have to do is ask him and trust him.
"Greg has been on the tour for 12 years. It doesn't make any sense. A young guy, perhaps, but why would a player as strong and as powerful as him need any assistance.
"I have to give him the benefit of the doubt."
The 29-year-old Spaniard, in Auckland as a wildcard for next week's Heineken Open, is in favour of the sport's drug-testing programme, but found it difficult to accept yesterday's report that Rusedski had tested positive for the steroid nandrolone following a test taken in July.
"It is not an easy situation," Corretja said. "Last year on the ATP tour they found something in samples taken from 40 guys. From nought to 40 in one year is strange."
He was adamant the players wanted no part of drugs in sport.
"We all agree we want it clean."
Corretja is in Auckland for the first time in seven years and looking to kick-start his year, and career, with a good showing before the Australian Open.
Asked whether he had been tested, Corretja said: "Many times, in and out of competition. I have no problem with that. I want to prove to other guys I'm not taking anything. In the last two years I have been tested more and more."
Somewhat ironically, the Heineken Open's top seed, Guillermo Coria, as a 19-year-old, was banned for six months from August 2001 after a controversial positive test, apparently related to Nandrolone.
There was a strong suggestion Coria was the victim of a "clouded test." He returned to the circuit, reaching No 45 by the end of the season.
Corretja, not surprisingly, was keener to talk about the sport, and particularly his game.
"It is nice to be back here and to be given a main draw wildcard.
"It has not been easy. At some time you reach a level when your body says stop a little bit. I have taken a break; now I'm ready to play."
At 3pm today (when the main draw is made) he will know who he will play first-up on Monday or Tuesday, and plan his comeback, as he looks to add to the US$10.1 million ($14.9 million) he has already pocketed on tour.
