The Gunners have strengthened the heart of their defence in recent windows, signing David Luiz, William Saliba and Pablo Mari, while Gabriel Magalhaes is expected to be announced imminently.
But Sardella was rejected, on the basis that Arsenal chiefs felt he was too small.
The 18-year-old featured 20 times in all competitions last season and plays for Belgium's under-21 side at present.
However, Sardella's father, Dino, explained how his performances weren't enough to earn a move to north London two years ago.
“Two years ago, Arsenal wanted to take him but it was to make him a defensive midfielder," he told Belgian outlet DH.
"The English club considered him too small to play behind [in the defence].
“At Anderlecht, it was never a problem. He has a big jump. It’s in the genes, thanks to my background as a volleyball player.
"Killian is also starting to build up a lot of muscles, that helps too.”
Sardella features at full-back but can also play in the centre of the defence.
And his father goes on to say his performances have earned him comparisons to Premier Legend Kompany, who currently coaches the youngster at Anderlecht.
“He had learned to appreciate the fullback position, but he still had a lot to learn. He was not as liberated as in the middle,” he explained.
“In the youth, he was often compared to Kompany because he was so comfortable with the ball at his feet.
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"A delegate who had Kompany and then Killian would tell me every time: ‘I think I’ll see Vincent again!’ The technical qualities are there.”
Arsenal are close to announcing Magalhaes in the coming days.
Meanwhile, Dani Ceballos is set to return to the Gunners on another season-long loan deal.