Daniel James' transfer value has skyrocketed to between €40million (£36.6m) and €50m (£45.8m), according to the CIES Football Observatory.
United paid Swansea £15m to sign the 21-year-old during the summer transfer window, a fee that could rise to £18m with add-ons.
The Football Observatory takes into account a number of factors before placing a value on a player.
These values include: Activity in clubs and national teams, club and national team results, age, position, league of employment, economic level of the releasing club, contract duration, year of transfer, book value, loan status, nationality and economic level of the recruiting club.
James came on as a second-half substitute for United against Chelsea on August 11 and scored the Reds' final goal in the 4-0 victory.
Scott McTominay has formed a close bond with James since the Welshman moved to the club in June and he was over the moon when his new friend found the back of the next on his competitive debut.
"I was so, so pleased for him," McTominay told the BBC. "That was probably one of the happiest I've been on a football pitch, seeing one of my pals score his first goal for the club because I was just made up for him.
"When I got home, I sent him a little text and said well done. He deserves it, he's such a hard-working lad, but he knows it's only the start.
"He says it's not just one goal that can be big for you, it's getting 50, 100, and he's very capable of that.
"As you're seeing he's done really well at the start of his Man United career."
