Schumacher, son of Ferrari great and seven-times world champion Michael, is out of contract at the end of the season with Haas considering their options.
"I think he’s been really improving over the year. He started off maybe not really liking the car and lacking a bit of confidence, but he’s really gained that," Magnussen told reporters ahead of Sunday's US Grand Prix.
"Lately he’s been super hard to beat for me. I think, the way he’s driving right now, he definitely deserves a place on the grid. But again, it’s totally out of my hands and I can only sort of wish him well."
Schumacher has scored in only two of 18 races, with 12 points to Magnussen's 22.
He was eighth in Britain and sixth in Austria but neither he nor Magnussen have scored in the last seven rounds.
Magnussen hoped Austin's Circuit of the Americas might be better suited to their car.
"I think we generally are more happy with high downforce tracks, and this is a high downforce track, so hopefully we can be a bit more competitive," he said.
"I think lately, some of the other teams have kind of moved ahead of us in terms of outright performance but that doesn’t mean we can’t fight them and have a chance against them."
