The former Celtic goalie's son Andy plays in the Govan club's backline.
McKenna had long chinned Bonner junior about getting his father to help out with Junior football's green and white hoops.
But never in his wildest dreams did he imagine the 80-times capped Irish shotstopper would actually turn up at McKenna Park.
NowMcKenna is hoping regular Ants keeper Matty Carr will gain inspiration from Bonnar's one-to-one coaching going into his side's epic Emirates Scottish Junior Cup clash at home to reigning West Region champions Irvine Meadow this Saturday.
The gaffer said: "To walk into the dressing room and have Packie Bonner mixing with our players was mind boggling. But he was more at ease with the situation than I was.
"I've been on young Andy's case, saying he should get his father to pass on a few tips to Matty.
"But that was more in jest than anything else as I couldn't contemplate someone who has been at the very top for club and country giving the Juniors a second thought.
"It speaks volumes for Packie that he was willing to come to a club like St Anthony's to lend us his great expertise. I'm convinced Matty will be all the better for working through several goalkeeping drills with the man.
"All the other players were understandably in awe of him, but he made them feel comfortable by joining in their routines to the extent that I was rubbing my eyes in disbelief towards the end of training at the sight of a seven-a side game being played with Matty in one goal and Packie Bonner in the other."
The long-serving gaffer admitted to a number of selection woes ahead of his side's David v Goliath contest.
Gary Dickson is not back from holiday until the end of this week, Steven Greenlees is cup-tied and Mark McCuish is suspended after being sent off against Lanark last Saturday.
Jordan White is struggling to shake off an injury and work commitments look like ruling out Bernie McDonald. McKenna said: "People would still look upon us as cannon fodder even with everyone fit and available, so we've nothing to lose in having a real go at Medda."
A definite non-starter for Medda is top scorer Richie Barr following his red-carding in last weekend's defeat by Glenafton, while Stevie Miller will not be considered after he was put up for transfer at his own request.
The midfield battler said: "There's no enjoyment from being on the sidelines most weeks without getting a look in, so it's probably best I move on. There's no hard feelings and I wish the guys all the best against St Anthony's in what could prove a very testing cup-tie."