The sickness sidelined the Jets quarterback last week and will so again this week. But after a bye next week, Darnold believes he'll return for New York's trip to Philadelphia in Week 5.
"I have full confidence that I'll be ready for the Eagles game," he told reporters Wednesday. "I'm not going to promise anything because I don't know where exactly this mono thing is going. But that's the goal that the doctors have set, and that's the goal I have set the game to be back for."
Darnold, who returned to the team facility Tuesday, has not been cleared to play. He merely hopes to begin running during the bye, noting that his spleen is still enlarged. But he's made considerable progress in just the last week.
"I'm just listening to my body," Darnold said. "When I get tired, if I have time, if I'm at home, I'll take a nap. You just got to listen to your body, that's what the doctors told me to do. ...
"I feel way better today. My energy's up. Not exactly where I'd like it to be by next week and other weeks, but it's been good, especially all things considered."
The second-year QB reiterated he wasn't feeling like himself in Week 1 against the Bills. Darnold managed to complete 28 of 41 passes but averaged a career-low 4.2 yards per attempt. His performance waned in the second half as the Jets were shut out in the fourth quarter while blowing a 16-point lead.
Since then, Darnold said he's used the unexpected downtime to study the offense, which is still relatively new to him under Adam Gase. After seeing Trevor Siemian go down with a season-ending ankle injury in Monday night's loss to the Browns, the 0-2 Jets will start Luke Falk against the Patriots this Sunday.
"I think so, given that mono can take a long time to run its course," Darold said. "It's definitely not something that I planned for and it's probably the worst timing. But it's something that you just got to deal with. As a player, some things, you get dealt the cards you get dealt. Right now it's just about trying get healthy and getting back out there."