Alex Partridge will join Matthew Pinsent, James Cracknell and Steve Williams in the coxless four for the first World Cup regatta of the year.
Partridge (right) and Andy Hodge won the British pairs trial
The 23-year-old, who with Andy Hodge won the pair at last week's British trials, takes over from Josh West.
The selection is a good indication of the Olympic squad, to be named in June.
"We are confident that this is a strong line-up with which to go forward into the racing season", said British Performance Director David Tanner.
Tanner added: "Alex thoroughly deserves his place in this lead boat."
Partridge, a world junior silver medallist in 1999 and world U23 medallist in 2000, won World Championship bronze last September as part of the British eight.
He said: "Before Christmas I was just worried whether I would make it to Athens or not.
"So, it's a bit of a shock suddenly being in this boat. Now I'm here and I am going to do the best I can".
Pinsent and Cracknell are defending Olympic champions in the coxless four after winning gold in Sydney with Sir Steve Redgrave and Tim Foster.
The duo then switched to the pair and became world champions in 2001 and 2002.
But in February, after a disappointing 2003 season, coach Jurgen Grobler moved them back to the coxless four with Williams and West - displacing Toby Garbett and Rick Dunn - in a bid to secure gold in Athens.
Pinsent, who missed the trials with tonsilitis, said: "It's so different to what's happened before in the lead up to every other Games I've been to.
"It's an exciting situation. We have no form as a crew, no-one knows how we are going to race. They don't know what our strengths and weaknesses are".
West, a 2002 and 2003 world coxless four silver medallist, competed with Williams in the pair at the British trials but they finished a disappointing fifth.
The full British team for the regatta in Poznan, Poland, from 7-9 May will be announced on 22 April.
The Olympic team will be named after the third and final World Cup regatta in Lucerne, Switzerland, on 24 June.