In the semifinals, actually Gasquet played singles and won also.
But, I don't see Gasquet as a good choice for singles against the Swiss Team.
They are required to submit a team of four players 10 days before the tie. Today is that deadline as the DCF Starts on 21st November. They don't have to declare who will play singles and who will play doubles at this time. They are allowed to change a maximum of two of the players in the team until one hour before the draw. The draw happens the day before the start of the tie and at least 24 hours before the commencement of play. Even at this time, they are not required to say who will play singles and who will play doubles.
They can fool around among the four selected players in the team and decide as to which two are going to play Singles on the opening day until 1 hour before the first match. Similarly, they only need to declare the players for doubles and reverse singles only one hour before the start of play on 2nd day and on 3rd day. Finally, they can change the player involved in the last singles match by announcing it within 10 minutes after the end of 4th rubber.
Also, there are exceptions to these rules based on injuries that occurred to players after the
team is announced and disciplinary actions against players, that are not worth describing further.