The latter was Jose Mourinho's primary midfielder target this summer and the Red Devils were willing to outlay up to £60m ($78.8m) to bring him to Old Trafford, but Mauricio Pochettino made it clear that Dier will not be sold this summer.
The Portuguese manager has made it clear that he wants to sign a defensive midfielder this summer and Matic is among a list of targets on the Red Devils boss' radar. Chelsea have signed Tiemoue Bakayoko from AS Monaco and the Frenchman is likely to partner his compatriot N'Golo Kante in midfield next season, which will limit the Serbian's game time.
Matic, who was a key member of Antonio Conte's title winning squad, is said to be looking for a move away this summer and United along with Juventus and Inter Milan have shown interest in signing him. The midfielder was omitted from Chelsea's pre-season squad to Asia and continues to train at Chelsea's Cobham training facility.
According to the Independent, Mourinho is keen on a reunion with his former player and United are set to make an official approach for the Serbia international. United will need to convince the Blues to sell to a direct rival and are aware that it will cost them upwards of £40m to complete the deal.
Apart from Matic, United were also linked with a move for Renato Sanches, who has been deemed surplus to requirements at Bayern Munich. Mourinho is a big admirer of the Portugal international and was keen to sign him last season before he joined the German champions. The United boss looks to have lost out for the second time as AC Milan are said to be close to finalising a deal for the midfielder.