One suggestion on the Formula One grapevine is that the 48-hour delay is due to continuing discussions over Mansell's personal sponsorship commitments and minor details of the one-year agreement.
There seems no doubt, however, that Mansell will sign for McLaren.
The 41-year-old, former world champion has been in negotiations with the Woking-based team since his former employers, Williams-Renault, chose the Scot David Coulthard to partner Damon Hill.
Mansell's agent, Sue Membury, said: "Negotiations are well advanced but nothing has been signed. If it had, we would be aware of it and it would be announced publicly."
After initially asking for $16m (£10m), the 1992 champion is understood to have settled for $10m from McLaren for the coming 16-race series, which is scheduled to start in Argentina on 12 March.
McLaren are the only major team yet to finalise their line-up, Benetton-Renault having confirmed on Monday that the 30-year-old Briton, Johnny Herbert, will partner the world champion, Germany's Michael Schumacher.Reuse content