Marcus Ericsson finds it "disappointing" not to be continuing in Sauber's Formula 1 race line-up in 2019 after being part of its recent revival, but remains proud of his involvement in turning the team's fortunes around.

Ericsson made his final appearance for Sauber in Abu Dhabi last month ahead of his move into IndyCar next year with Schmidt Peterson Motorsports, having spent four seasons with the Swiss team.

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In that time, Ericsson saw the team drop to the back of the field and face financial uncertainty, only to enjoy a resurgence this year after securing a fresh partnership with Alfa Romeo, allowing the Swede to enjoy his most regular point-scoring season in F1.

While Ericsson expressed his pride over Sauber's upturn in fortunes and the role he has played in it, he conceded it was difficult he could not continue to reap the rewards in 2019 after the team opted to sign Antonio Giovinazzi and Kimi Raikkonen to its race seats.

"That’s the disappointing part, not being able to continue it," Ericsson said.

"I’ve been here throughout all the bad times, and then now through the good times this year, and I feel very much part of the journey with the team, with everything that’s been happening.

"That’s why it’s sad not to continue with that, because now it really feels like we’re starting to hit out stride as a team and we really starting to fight higher up the field.

"[It] would have been nice to continue that for next year, but that’s the way it is. I’m still proud of what I’ve done and I feel I’ve been very much part of what the team has become today."

Ericsson is set to retain a role with Sauber next year in tandem with his IndyCar racing commitments, acting as the team's reserve driver, but said the exact details of his involvement are still to be defined.

"We need to still sit down after the season and discuss that as I made it very clear that I want to focus 100 percent on a racing programme for 2019, and when I had this IndyCar option I wanted to go all in on that," Ericsson said.

"I’m still happy to be able to keep a connection to the team, but I need to sit down with the team and see exactly what I will do or not do and what my role will be.

"But for sure, 110 percent focus needs to be on IndyCar, otherwise there’s no point going there if you’re not 100 percent committed for it."