Manchester United agreed personal terms with the 27-year-old and struck a deal with Atalanta worth up to £38million in early June, with the Brazil international having appeared to view the move as all-but confirmed during his time at the World Cup.
According to Fabrizio Romano, however, an underlying knee issue has complicated the transfer following a medical examination in the UK, with reports suggesting scans have raised questions about a long-term problem stemming from a previous meniscus injury.
Multiple reports on Friday evening indicated that Ederson would not, after all, be heading to Old Trafford, but Manchester Evening News reports the club do not consider the move to be off, even as they carry out further checks before reaching a final decision.
Ederson had originally been a summer target for Atletico Madrid before United moved to hijack the deal, while the Spanish club turned their attention instead to Wolves midfielder Joao Gomes, a move that also now appears to have collapsed.
United have scouted Ederson previously during his four years at Atalanta and had looked poised to sign him as part of a wider overhaul of Michael Carrick's midfield this summer.
Signing an elite-level number six to replace Casemiro remains United's priority, with Real Madrid's Aurelien Tchouameni among the leading alternative targets, while Bournemouth's Alex Scott and Borussia Dortmund's Felix Nmecha have also been mentioned as contingency options should the Ederson deal ultimately fall through.
United are also edging closer to a separate £48million deal for Chelsea midfielder Andrey Santos, regardless of how the Ederson situation is resolved.
The uncertainty comes as an unwelcome complication for United, who have already missed out on several other midfield targets this summer, including Elliot Anderson, Mateus Fernandes and Sandro Tonali.
Should the club ultimately walk away from the deal, they would be forced to move quickly to identify alternatives before the window closes, having viewed Ederson as a value addition given the relatively modest fee involved compared with the other names on their shortlist.