New to the squad is Ireland Under-19 midfielder Luca Connell. The Liverpool-born youngster - who broke into the first team set-up at Bolton Wanderers this season - featured in last year's UEFA European Under-17 Championships.
"Luca deserves this opportunity," said McCarthy as he brings his squad to Faro, Portugal for a training camp ahead of the two Group D qualifiers.
"With midfielders Conor Hourihane, Glenn Whelan and Josh Cullen all on play-off duty with their clubs in the coming weeks, this is the perfect chance to get Luca into the squad.
"He has had a fine season with Bolton playing 15 times in total and even with their relegation troubles, he has impressed so many people. I know a number of big clubs have sent scouts to watch him so this is a chance to get him in to work with the senior players and see how he gets on."
McCarthy has cut his provisional squad down to 27 players, with 23 travelling to Portugal and the play-off quartet of Richard Keogh, Glenn Whelan, Conor Hourihane, and Josh Cullen set to join up in Dublin before the trip to Denmark.
Norway-based goalkeeper Sean McDermott comes in for the injured Kieran O’Hara, while Harry Arter, Jack Byrne, James Collins and Aiden O’Brien miss out.
The Irish players and management will gather in Faro from Tuesday with the Championship and League One play-offs now on their television schedule.
"We will miss the lads in Portugal but we will be tuning into their games," said McCarthy as he revealed his final squad to FAI.ie.
"I’m sure there will be divided loyalties when Glenn and Conor take on Richard but Josh might get a clean run at the support of the squad when Charlton play Sunderland.
"The benefit for us is that the four lads will be firing on all cylinders when they join up with the rest of the group in Dublin at the end of the month."
Preston North End duo Callum Robinson and Alan Browne, Bristol City’s Callum O’Dowda and Southampton striker Shane Long all travel to Portugal after returning to fitness, while Cardiff City defender Greg Cunningham and Aston Villa’s Scott Hogan feature under McCarthy for the first time.
Republic of Ireland Squad
Goalkeepers: Darren Randolph (Middlesbrough), Mark Travers (Bournemouth), Sean McDermott (Kristiansund BK)
Defenders: Seamus Coleman (Everton), Matt Doherty (Wolverhampton Wanderers), John Egan (Sheffield United), Kevin Long (Burnley), Richard Keogh (Derby County), Shane Duffy (Brighton & Hove Albion), Enda Stevens (Sheffield United), Greg Cunningham (Cardiff City)
Midfielders: Alan Judge (Ipswich Town), Alan Browne (Preston North End), Glenn Whelan (Aston Villa), Jeff Hendrick (Burnley), Conor Hourihane (Aston Villa), Luca Connell (Bolton Wanderers), Josh Cullen (Charlton Athletic*), Robbie Brady (Burnley), Callum O'Dowda (Bristol City), James McClean (Stoke City), Ronan Curtis (Portsmouth)
Forwards: David McGoldrick (Sheffield United), Shane Long (Southampton), Sean Maguire (Preston North End), Scott Hogan (Aston Villa), Callum Robinson (Preston North End)
*Indicates the player is on loan