Saad was not originally named in the Saints' 25-man squad on Thursday, but was rushed to Brisbane as an emergency replacement for Trent Dennis-Lane on Friday night.
He was then inserted to the starting 18 on the day of the match to replace the ill Jack Newnes.
Saad was named on Wednesday as being under investigation by the AFL for an alleged breach of the anti-doping code for taking a substance permitted for use "out of competition."
Until the sample results of both tests have returned, no action can be taken and Saad is eligible for selection.
Rather than sneaking Saad into Brisbane to avoid the media spotlight, Watters said the set of circumstances that gave the small forward his opportunity was all above board.
"We pick our side and like every club we have the opportunity to change emergencies as we go," Watters said.
"The process ... is AFL approved and we followed that to the letter.
"The reason why Jack Newnes, Trent Dennis-Lane, Seb Ross, who were emergencies, don't play, is they were crook as dogs for 24-48 hours.
"Pretty good shot of gastro going through our boys."
Watters said both Rhys Stanley – who was subbed off at half-time with a collarbone injury that will be scanned on Sunday – and Ben McEvoy played with the bug.
While describing Saad's three-disposal, two-goal game as "average", Watters said he was not prepared to speculate further.
"It's confidential," he said.
"That whole situation, and unlike many throughout the press I'll maintain that level of confidentiality on that situation, as the code actually demands, so there'll be no comment."
On Friday an AFL spokesperson said the League was yet to receive the results of Saad's B-sample.
If charged, Saad would face an AFL Tribunal hearing. Under the anti-doping code, use or possession of a prohibited substance can lead to a two-year ban for a first violation.
Watters said despite losing to the Lions by 31 points, playing under physical duress was something that would hold his team in good stead.
"They're still great experiences for players to go through, because if that's a final, you've got to find a way to play so I was rapt with what some of them did," he said.
Michael Whiting is a reporter for AFL Media. You can follow him on Twitter: @AFL_mikewhiting
