Manchester United boss Jose Mourinho sent scouts to watch Glasgow Celtic's Kieran Tierney during the Hoops' 4-0 annihilation of Glasgow Rangers in the Scottish Cup semi-final at Hampden Park on Sunday afternoon, according to reports. 

The Portuguese manager is keen to find a long-term left back with Ashley Young entering the twilight years of his career and Luke Shaw seemingly not fitting the bill at Old Trafford. 

And according to The Times, the Red Devils manager has identified the Hoops starlet as a possible solution, with the Old Trafford talent spotters watching on as the 20-year-old's outfit booked their final spot against Motherwell next month. 

Tierney has hugely impressed under the stewardship of Brendan Rodgers at Parkhead and is seen by the Northern Irishman as well as the Bhoys hierarchy as a player for the future. 

However, the United contingent are hoping they can persuade the Scotland international to leave his boyhood club in favour of a spot south of the border. 

Sunday was not the first time Mourinho has sent his scouts to watch over the highly promising defender, with the youngster already recording 27 European appearances; 21 of which being in the Champions League, a cause for significant interest from the north west giants. 

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The Red Devils were traditionally known for having a long-term left back in place under Sir Alex Ferguson, with Denis Irwin making 368 appearances for the Red Devils over 12 years and Patrice Evra playing 275 times over a similar period. 

However, since his departure, Shaw has failed to live up to expectations at Old Trafford while Young, who has enjoyed a superb campaign this term, being right-footed provides an unbalance down the flank. 

It is thought, however, that Manchester United would be forced to outlay a significant fee to land Tierney, who signed a new six-year contract with Celtic last year.