Cavani arrived in Manchester on Sunday ahead of final talks and medical tests at Carrington. The 33-year-old is set to sign an initial one-year contract with the option of another 12 months.
Telles should follow the Uruguayan in at Old Trafford ahead of Monday's transfer deadline after sources told ESPN United are in advanced negotiations over a deal for the Brazilian left-back.
Porto have accepted a bid of around €15 million plus add-ons after initially demanding closer to €20m up front. The 27-year-old is scheduled to undergo a medical before joining up with the Brazil national team.
United turned down the chance to sign Cavani in January after being put off by his wage demands of £360,000-a-week. After leaving Paris Saint-Germain in the summer, the striker has been offered to every major club in Europe before United stepped up their interest last week.
Sources have told ESPN his wages will be significantly lower than his demands in January and the agent fees involved in the deal will be lower than €10m.
United were keen to tie up a deal for a centre forward knowing that Odion Ighalo loan from Shanghai Shenhua is set to end in January.