Both Gilbert and Ewan – who signed a two-year contract extension in front of the media at Lotto Soudal's team camp on Wednesday – head into 2020 looking for their first-ever win in Milan-San Remo.
Ewan has finished second in the Italian Classic, while Gilbert has won every Monument bar La Classicissima during his already glittering career.
"If the race goes in the direction in which Phil is going to win, then I'm not going to be there because it will be too hard for me," Ewan told the media at Lotto Soudal's camp in Mallorca, Spain.
"However, if the race is easier and I'm there then Phil is not going to win because he needs a hard race. It's great that we're going into the race with two options."
Ewan will follow a typical race programme for the first half of 2020. He will skip the Bay Crits and Australian nationals and line up at the Tour Down Under in January. Milan-San Remo is his first major target of the campaign before his focus turns to the Giro d'Italia and the Tour de France.
He may race a handful of the Belgian one-day races in the spring but, with Gilbert and John Degenkolb now on Lotto Soudal's books, the demand for the Australian in the cobbled classics will be relatively low - hence why San Remo is such a huge focus for the pocket-rocket sprinter.
"It's the biggest Classic that I'll do in the year. It's the only Monument that a pure sprinter can win, so if there's a Monument I want to target in the year, it's that one. That makes it special."
Ewan also believes that the arrival of Gilbert will lift the pressure on his own shoulders when it comes to major objectives.
"We both live in Monaco so I knew him before he came to the team. I'm happy to have a guy of that much experience in the team," he said.
"I came in last year at 24 but as one of the main leaders so I didn't have that much experience of being a leader, so having a guy Phil coming into the team, I can learn a lot from him."
Lotto Soudal also used Wednesday's press conference to announce that Ewan would be extending his contract with the team for an additional two years beyond 2020. He signed his new contract in front of a gathering of journalists and the Lotto Soudal management and then explained his reasons for re-signing.
"When I signed with the team you're not sure how it's going to go in the first few years," he said.
"Straight away, in the first few months, I knew that I was happy and that I fitted in. There were some moments at the start of the year when it wasn't going so well but the team backed me at the time and that gave me the feeling that the team were always going to support me. Then when I started doing well that really cemented the fact that I wanted to stay in the team. Their ambitions match mine."
Ewan's lead-out riders, Jasper De Buyst and Roger Kluge, also signed two-year contract extensions.