Jose Mourinho is widely expected to take the reins at Old Trafford in the next few days following Louis van Gaal's sacking.
Italian website Calciomercato claim Mendes promised Gomes' services to Mourinho wherever he managed next season.
And media outlet Fichajes claim Mourinho is still eyeing a swoop for his fellow countryman.
Valencia have suffered a torrid season and it's widely expected that they'll struggle to keep hold of their star men.
Garay is an experienced campaigner and has been capped 32 times for Argentina.
The commanding centre-back spent three years at Real Madrid before being offloaded to Benfica in 2011.
He left the Portuguese club in 2014 for £4.6m.
But it's claimed United will need to spend over £19.4m to secure his services from the Russian giants.
The Red Devils have also been linked with moves for Everton defensive duo John Stones and Seamus Coleman.
