After establishing himself as one of the best defenders in the league under former United boss Louis van Gaal, Smalling has found his opportunities limited under Mourinho, making just 18 Premier League appearances for the Red Devils last term.
Daley Blind and Marcos Rojo have often been preferred by the Portuguese and with Eric Bailly’s return from injury and United’s £30m summer signing of Benfica’s Victor Lindelof, Smalling may well need to leave Old Trafford to play regularly next season.
Baggies boss Tony Pulis is reportedly an admirer of the 27-year-old and sees the England international as an ideal addition to West Brom’s back-line.
West Brom secured a superb tenth placed finish last season, but the Baggies will be disappointed at the team’s decline in form after the 40-point mark was assured and will be keen to bring an experienced competitor like Smalling.
Pulis’ former club Stoke, as well as Leicester and Crystal Palace are also reportedly interested in the former Fulham centre-half.
West Brom have signed former United stars Darren Fletcher and Jonny Evans in recent years and look set to offer £10m to bring the former Millwall youth player to the Hawthorns.
"We have three or four other targets we are desperate for. We are juggling with two at the moment and that’s not [Kieran] Gibbs," he said.
“Hopefully by the time we get back home we will have done those two.”