Keith Millen was in the dugout for the Gills, but endured a moment to forget before the half-hour mark when he brought down the winger.
The incident happened after a diagonal pass was played from the Walsall defence and intercepted by Gillingham defender Shadrach Ogie.
With Knowles looking to take a quick throw-in in front of the dugouts, Millen stuck out a leg and tripped the winger.
This led to referee Charles Breakspear to promptly walk over and brandish the red card.
While it remains to be seen if Millen tripped the player on purpose, it's clear that his attempts to time-waste backfired badly.
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With the scores 0-0 at the time, things went downhill quickly for Gillingham.
They conceded two goals in the ten minutes that followed, leaving them 2-0 down at half-time.
Things got worse when Isaac Hutchinson got his second for Walsall in the 58th minute, before Macauley Bonne clawed one back for the Gills moments later.
However Hutchinson completed his hat-trick five minutes from time to condemn Gillingham to a 4-1 defeat on a disastrous day at the Bescot Stadium.
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The Kent-based side are looking for a new manager following the decision to sack Neil Harris.
The ex-Millwall and Cardiff boss lost his job despite the Gills sitting sixth in League Two.
Their defeat away at Walsall leaves them seventh in the League Two table.
Though incredibly, they sit just four points behind leaders Stockport.