Manchester United are reportedly considering a move for Borussia Dortmund ace Julian Weigl after missing out on their top two midfield targets.
Chelsea are said to be playing hardball when it comes to selling Matic to a direct Premier League title rival, however, while Tottenham Hotspur are also reluctant to offload versatile Englishman Dier.
Mourinho may now have to look further down his transfer wishlist, according to the Daily Mail, which could mean making an offer for Weigl.
The 21-year-old is a regular at Dortmund, featuring 43 times in all last season, but he is expected to miss the opening month of the new campaign due to a broken ankle sustained in May.
It is claimed in the same report that Chelsea could change their stance on Matic, however, should a deal for Tiemoue Bakayoko be finalised before the August 31 deadline.