Barcelona made three offers for the Brazilian star – all of which were rejected by Chelsea – before they raided Bordeaux to sign Malcom.
Chelsea appear in no rush to sell the 29-year-old, who was arguably Brazil’s best player at the World Cup.
But Sheth thinks there is a chance United could now move with Barcelona potentially taking their interest elsewhere.
Speaking on the Sky Sports Transfer Talk podcast Sheth said: “We’ve been talking about a likely forward position because we know they’re interested in Willian.
“They were interested in Willian earlier on in this window then the whole Barcelona thing came about when they made three bids, the latest in excess of £55m.
“But that’s now got a twist and a development in regards to Barcelona because it looks like Malcom is going to be finalising his deal to the Nou Camp from Bordeaux.
“He was all set to go to Roma wasn’t he? That was a strange one. Almost a U-turn when Barcelona came about and it looks like he’s going to be a Barcelona player.
“I wonder if that ends Barcelona’s interest in Willian. And I wonder if that re-opens the door for Manchester United and Willian.
“It just seems to me that United over the last two years, potentially over the last four years since Sir Alex Ferguson retired the balance of the squad is the one big talking point and the one big issue that successive managers have had.”
Former Chelsea manager Jose Mourinho is still interested in a reunion with Willian at United, but the Blues don’t want to sell to a Premier League rival.
Chelsea director Marina Granovskaia and owner Roman Abramovich met this week to discuss possible departures and signings by new manager Maurizio Sarri.
A source close to Willian said this week: “The Barcelona bid has been rejected for now – let’s see what happens.”