The former Dundee United playmaker could yet take on Jose Mourinho’s Chelsea after Sporting boss Marco Silva included him in the club’s 25-man group.
That seemed unlikely after the Scotland Under-21 international was sent to play with their second string following his £3million summer move from Tannadice.
But UEFA has now confirmed to Press Association Sport that Gauld has been named in the 18-time Portuguese champions’ squad for the tournament, with the teenager handed the number 27 shirt.
As well as Barclays Premier League leaders Chelsea, Sporting are also due to take on Germany’s Schalke and Slovenian’s Maribor - who knocked out Scottish champions Celtic in the qualifiers - in Group G.
Sporting announced last month that the 18-year-old would drop down to their B team but Gauld insists the move will only help him develop.
The former United youngster - who is due to start for Billy Stark’s Scotland youngsters in Slovakia on Thursday - told the Daily Record: “There’s not really a deadline for me to push for the first team but it’s going to take longer than some people think. Sporting are a Champions League club, after all.
“I don’t understand people thinking I was going to go over there and just walk into that team. It seemed to be the expectation of many.
“However, this was the way I pictured it would be and everything is going the way I expected.
“Saying I have been demoted to the B team is false. That was always the plan, arranged from the start, and the quickest way to help me adapt to Portuguese football.”