Manchester United manager Louis van Gaal reportedly sent a scout to watch two of Barcelona's young players in Copa del Rey action last night.
The main focus of attention is believed to be midfielder Sergi Samper, who played the entire 90 minutes of the 0-0 draw away at third-tier Villanovense.
According to the Daily Star, the 20-year-old has a release clause in his contract at Camp Nou that is valued at £8.5m.
It has been suggested that Samper is highly regarded by Barca head coach Luis Enrique and his staff, but he has struggled to nail down a spot in the starting lineup.
The report adds that debutant Wilfrid Kaptoum was also a subject of interest from the United's watching representative.