Spanish media outlet AS, as quoted by the Daily Express, is reporting that Manchester United have idenitified the 24-year-old as a player who could replace Pogba.
The same article states that Ole Gunnar Solskjaer has made Saul their number one target should Pogba force a move to Juventus or Real Madrid before the start of the new season.
According to the same story, the 20-time English champions have already contact4ed Atletico Madrid about the possibility of bringing Saul to Old Trafford this summer.
The report goes on to add that Saul has a £134.5m (€150m) contract release clause that Manchester United could avail of if the Red Devils are willing to make the midfielder this most expensive signing.
Manchester United could find it difficult to secure a deal for Niguez given that he has seven years left to run on his current deal at the Spanish side.
The Red Devils have already made two summer signings this season.
Manchester United signed Wales international Daniel James in a £15m deal from Championship side Swansea City.
The 20-time English champions finally complete a £50m deal for Aaron Wan-Bissaka last weekend.
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