The club is hopeful of signing the midfielder in the next 48 hours.
Sky Sports report that United today triggered the 29-year-old's £4.5million release clause.
Diame has a year left on his contract at the KCOM Stadium and is understood to be interested in a move to Newcastle.
The Senegal international is wanted as a replacement for Moussa Sissoko, who is set to leave St James's Park.
Sissoko, rated in the £35million-bracket, is wanted by Real Madrid.
And reports in Spain today claimed the club had opened formal talks with Newcastle over Sissoko, who was due back on Tyneside today.