The Portuguese giants know they are facing a battle to keep the Serbian midfielder at the club in January, and are looking to recoup around £20million by selling him.
The club claim there is strong interest in the former Chelsea reserve, who joined Benfica as part of the deal which saw David Luiz move to Stamford Bridge.
Manchester United and Borussia Dortmund are believed to be among those interested, and are set to test Benfica’s resolve with a January bid.
United remain desperate to strengthen their midfield in January, after a summer spent failing to sign targets which has had a negative impact on their season so far.
Moyes saw his side slip to their fourth Premier League defeat of the season last night, going down to a 1-0 home defeat to former club Everton.
The result left Manchester United 12 points off league leaders Arsenal, and was another game in which the club’s only major summer signing Marouane Fellaini failed to make an impact.
The Belgian arrived at Old Trafford for £27.5million after Moyes missed out on the likes of Cesc Fabregas, Thiago Alcantara and Ander Herrera in the summer.
Fellaini has struggled to settle however, and United are currently without influential midfielder Michael Carrick until after Christmas.