United spent a world record £30m for a teenage Shaw in 2014, but the former Southampton has struggled with fitness and injuries - most notably a broken leg - throughout his time at the club.
As such, the club has been heavily linked with various left-backs, including Danny Rose, Alex Sandro, Ryan Sessegnon and Kieran Tierney, while Shaw has equally been linked with a move away to clubs like Tottenham and even Liverpool.
But Mourinho hinted last month that the 22-year-old has a long-term future at United when he insisted that he effectively labelled Shaw one of the best left-backs in the world on current form.
Now, speaking ahead of United's Premier League trip to Newcastle on Sunday, Mourinho has publicly put his faith in Shaw even more.
Jose on @LukeShaw23: "He has been, for a few months, free of minor injuries that can stop [a player's] evolution and I'm really happy [with him]. I think he will be a Manchester United player for years." #MUFC pic.twitter.com/fXZAN7RzkJ— Manchester United (@ManUtd) February 9, 2018
"He has been, for a few months, free of minor injuries that can stop [a player's] evolution and I'm really happy [with him]. I think he will be a Manchester United player for years," the boss said.
Since handing the player his first Premier League appearance of the season in mid-December, Mourinho has carefully controlled which games Shaw has played. He's started seven of the last nine games in all competitions, but was left out of recent clashes with Burnley and Spurs.
He is set to keep his place in the line-up this weekend after being recalled against Huddersfield.
Luke Shaw has played a full 90 minutes in 7 of #MUFC's last 9 games in all competitions, and now Mourinho has declared he will 'be a Manchester United player for years'. Hard work finally paying off for him.— Jamie Spencer (@jamiespencer155) February 9, 2018
"They had a very good transfer window with Kenedy and Islam Slimani [arriving]. They are two players I know very well and they can really improve their team. Rafael Benitez knows how to get points, so I think it will be a difficult game," the Portuguese said.