The influential Danish international has endured an injury-disrupted season and was forced out of the semi-final second-leg against Bournemouth last weekend after aggravating an issue in the warm-up.
The Bees were due to make a late call on his availability on Friday and Thomas Frank has opted against naming him in his starting XI.
That means the west Londoners line up with the same side that started the comeback win over the Cherries, with Bryan Mbuemo preferred to Marcus Forss in attack, despite the latter scoring the goal which booked a trip to Wembley off the bench.
Brentford remain without star full-back Rico Henry and England U21 international Josh Dasilva because of long term problems.
Swansea are without 36-year-old Wayne Routledge, who may have played his final game for the club with his contract expiring.
Brentford XI: Raya, Dalsgaard, Jansson, Pinnock, Roerslev, Janelt, Jensen, Marcondes, Canos, Mbeumo, Toney.
Swansea XI: Woodman, Naughton, Cabango, Guehi, Bidwell, Fulton, Grimes, Hourihane, Roberts, Ayew, Lowe.