​Manchester United have reportedly taken their hunt for a new left back to the next level., as they are set to send a scout to Hampden Park to run the rule over Celtic starlet Kieran Tierney during the Old Firm derby on Sunday.

Celtic's rising star has earned interest from a host of clubs following a sensational start to life in Scottish football over the last three seasons, and the Red Devils are hoping to edge out their rivals in the summer in the race for the 20-year-old. 

Rangers v Celtic - Ladbrokes Scottish Premiership

Manager Jose Mourinho had visited Hampden Park last month to watch Scotland's international friendly against Costa Rica in a scouting mission for Tierney, who foiled his plans after withdrawing from the squad - as per the ​Daily Mail

The defender had been recommended to Mourinho by United's scouts after the manager told the club's executive vice-chairman Ed Woodward that a new left back was a priority in the next transfer window, due to the persistent issues troubling Luke Shaw. 

The England international has been sent down the pecking order in recent weeks in favour of Ashley Young, ​sending transfer speculation into overdrive as his relationship with Mourinho continues to be brought into question. 

Mourinho's visit to Scotland last month saw him meet with Scotland boss Craig Brown, where the pair were said to have discussed Tierney's development. 

The 20-year-old - with nine senior international caps - would prove to be a versatile option for United as he can also operate as a centre back. However, he remains far from the final product, which could lead United to considering the left back as a long term prospect for their defensive line. 

In other news, Mourinho ruled out signing another striker in the summer as competition for Romelu Lukaku as he already has Anthony Martial and Marcus Rashford as reserves for his position.