Kevin Magnussen should not give up on winning races and even the world championship.
Recently, Magnussen said: "I don't see myself as one of the young drivers on the way up anymore.
"You see drivers like Hulkenberg and other guys, great talents but no podium and never getting that chance. I'm in that group now," he added.
But Steiner urged Magnussen to keep believing.
"He could do two fantastic seasons and we still don't know what's happening in 2021," he told BT newspaper, referring to the expected major rule changes.
"It may be that an opening comes up at a big team, and if that happens, we would be the first to support him," Steiner added.
"We have always believed in him, and we will be proud if someday he became world champion. Even better, the new rules could mean he wins a race for us," he said.
Alongside Romain Grosjean, Magnussen has impressed Haas in the last two years but Steiner insists there is no 'number 1' driver.
"If the number 2 is happy to be number 2, he may not push the number 1 anymore and we don't need that. We are only in our fourth season and still need to grow," he said.
That said, he hails Magnussen's recent development as a driver.
"He's become more stable mentally," said Steiner. "The first two years in F1 were tough for him, because there was never really any stability, but he found that with us.
"He trusts us as human beings and has stopped thinking about what risks he is taking and what can go wrong."