Nelson has missed the entire season after injuring his shoulder while sliding back to first base during a game against the Chicago Cubs last September.
In Chicago before the Brewers' game against the Cubs, Milwaukee general manager David Stearns told reporters "it's fair to say we're running short of time" for Nelson to return, and manager Craig Counsell said Nelson "pitching for us this year is unlikely."
Nelson underwent surgery to repair his partially torn labrum, shoulder capsule and rotator cuff last September and has had regular checkups with Dr. Neal ElAttrache. Nelson hasn't been cleared to pitch off a mound.
"It's not a situation where you push him to get through it," Counsell told reporters, according to MLB.com. "He has to be 100 percent healthy. ... The way it's been set up is, 'Here's the hurdle, cross it, get to the next one. Here's the schedule, get there then do the next thing.'
"That will continue. The reason I'm saying this is where we're at in the schedule, he's not going to be able to pitch in major league games."
Nelson, 29, went 12-6 and led the team with a 3.49 ERA and 199 strikeouts in 175⅓ innings before his surgery last season. He has two more seasons of arbitration eligibility before he can become an unrestricted free agent in 2021.