The Red Devils lost 2-1 to Champions League holders Real Madrid in the Uefa Super Cup in Macedonia on Tuesday night.
Manchester United signing Romelu Lukaku halved the deficit with a close-range finish following goals from Casemiro and Isco.
The Europa League winners have been in the market to sign Croatia international Ivan Perisic from Inter Milan throughout the summer transfer window.
However, Manchester United temporarily switched their focus to Real Madrid forward Gareth Bale amid speculation about the Wales international’s future.
But Jose Mourinho ruled out the 28-year-old moving to Manchester United in the summer transfer window following Tuesday night’s 2-1 loss to Real Madrid.
BBC reporter Stone confirmed that the Red Devils are still in the market to sign a wide player ahead of the start of the 2017-18 Premier League season.
“He wants this wide player,” Stone told BBC Radio 5 Live.
“I still expect Mourinho to make another offensive signing, He will then think he has a squad capable of challenging for the title.”
Manchester United signed Victor Lindelof in a £30.7m deal from Portuguese champions Benfica in June.
The Red Devils spent £75m on Belgium international Romelu Lukaku from Everton last month to see off challenge from Chelsea.
Nemanja Matic made the controversial switch to Manchester United from the Premier League champions last week.
MORE: Man United latest news
MORE: Arsenal latest news
MORE: Chelsea latest news
MORE: Liverpool latest news