Having made my player British, I successfully got him to #2 ranking and partnered Andy Murray to bring home the Davis Cup!
Then, the next year, in the 1st round, UK plays Italy. I win the 1st game, but Andy loses - in fact he has to retire as he got injured. As Andy is also a doubles player (my player isn't), Italy has a W/O as they also do in Andy's 2nd singles - this means UK lost 2-3.
I don't know how easy this is, but Davis Cup needs setting up differently to be realistic. Davis Cup are teams of four players and any of these can play singles or doubles. In these circumstances, either my player or the 4th player would have played the doubles, while the other singles would have been played by either of the other 2 players.
Also, it shouldn't be necessary to "enter" the doubles as well as singles - you should just enter Davis Cup.
I suspect this won't be simple to do but it needs looking at, I think.