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The 23-year-old found himself out from the peloton on the left-hand side of the road with 140 kilometres to go in the race as he tried to use the extra width to move up in position.
But the road narrowed as he tried to do so, and Maciejuk was forced to ride into a puddle on the ensuing grass section, causing him to lose control of his bike and veer directly into a UAE Team Emirates rider at the front of the peloton.
The move caused a domino effect, as riders hit the ground hard one after another and the middle of the bunch was suddenly on the deck all over the road, Maciejuk managing to stay up despite bringing down so many others.
Wout van Aert (Jumbo-Visma), Julian Alaphilippe (Soudal-QuickStep) and Peter Sagan (TotalEnergies) were among those brought down, with the latter forced to withdraw from what was his final Tour of Flanders.
While Maciejuk continued, he was later called back and disqualified after the race referee reviewed the footage, the Pole later apologising via his Twitter account for the rash manoeuvre.
"I’m really sorry for my mistake and causing the crash today," Maciejuk said.
"I hope all those involved are in good health and safe.This should not happen and was a big error in my judgement."
The crash was the biggest out of many in what was the fastest edition of the 273.4 kilometre classic, as multiple riders were brought down in another fall with 71 kilometres to go including Biniam Girmay (Intermarche-Wanty-Gobert) who was rushed to hospital in the aftermath.
Last year's Gent-Wevelgem winner was the first to fall and looked unresponsive in the immediate moments after, but his team provided a promising update after the race.
