Manchester United must up their bid to sign Penarol fullback Guillermo Valera.
Valera enjoyed successful post-season trials with United last month.
There are reports of a â‚¬1.5million bid from the Reds, with various incentives.
Vice-president Edgard Welker told Futbol a lo Penarol: "It's an important offer. It's complicated - it's not easy."
The Penarol board rejected this first bid but are open to negotiation.