Tottenham had appeared close to completing the switch, with Richarlison poised to move to Goodison Park in a separate, related deal, after Roberto De Zerbi's side pushed hard for Ndiaye once Manchester City turned their attention to Liverpool's Cody Gakpo instead of the Senegal international.
A fee of around £60m has reportedly been agreed in principle between Tottenham and Everton, but with personal terms yet to be finalised, the door has remained open for a rival to intervene.
According to Senegalese outlet Taggat, Arsenal have done exactly that, reaching out to gauge Ndiaye's situation and explore whether they might tempt him to the Emirates instead. The interest comes as Arsenal continue reshaping their own forward line, having sanctioned exits for Gabriel Jesus to Barcelona and Gabriel Martinelli to Al-Hilal, and after missing out on alternative attacking targets including Morgan Rogers and Vinícius Júnior earlier in the window.
The club's headline pursuit of Julián Álvarez, meanwhile, appears to have stalled, with the Argentine understood to have his heart set on a move to Barcelona rather than north London.
Whether Arsenal's late approach amounts to a serious threat to Tottenham's deal remains to be seen, but with personal terms still unresolved and less than 48 hours left before the window closes, even a fresh conversation from a direct rival is enough to inject genuine uncertainty into a move that had looked close to completion.
Ndiaye, 26, has spent much of the summer attracting interest from across the Premier League's top clubs after making clear he had no intention of signing a new contract at Everton, and his versatility across the front line - comfortable through the middle or from wide areas - has made him a natural fit for several sides searching for late reinforcements.
Should Arsenal genuinely pursue him, it would represent a significant escalation of the north London rivalry in the closing hours of the window, with Tottenham having invested considerable effort in agreeing the framework of a deal only to face a late scramble to see it through.