Fredette, the leading scorer in the Mountain West Conference at 20.6 ppg, played only 16 minutes in Saturday's 83-81 loss to New Mexico.
"He just really became nauseated, pains in his stomach and he didn't hardly eat anything in the pregame meal. He just wasn't himself," Rose said.
Rose sat Fredette the final 19 minutes after noticing his star guard was low on energy.
"I could tell that he was really struggling, and those are some of the hardest decisions you make as a coach," Rose said.
At this point team doctors believe Fredette is suffering from some sort of a stomach virus or the flu. They don't believe he's having a relapse from his bout earlier this season with mononucleosis.
"Hopefully he'll be able to knock this out," Rose said.
Fredette received fluids through an IV on Monday and did not practice. He is expected to practice on Tuesday. It's unsure if, or for how many minutes, he'll play on Wednesday at the Huntsman Center.
"I really feel for Jimmer because he's had a tough season. He's dealt with a lot of things," Rose said. "But hopefully he'll be better and we'll get some play out of him this week. But more importantly get him ready for three games in a row in Vegas (at the MWC Tournament next week) if we can win."
Fredette has already missed two games this season because of illness, and played limited minutes in two other games.
LITTLE DAMAGE IN THE POLLS: Despite Saturday's loss to New Mexico, the Cougars (26-4, 11-3) dropped only one spot in the AP men's basketball poll released Monday, and three spots in the ESPN/USA Today coaches poll. They are now ranked No. 14 in the AP poll and No. 15 in the coaches poll.
"It says that they're a really good team, and that they're respected around the country obviously by the people who vote," Rose said of the Lobos, who ended BYU's 21-game home winning streak.
New Mexico, which clinched at least a share of the MWC championship, moved up to No. 8 in the AP poll and No. 10 in the coaches poll. The Lobos are 27-3 overall and 13-2 in league play with only a home game Wednesday against TCU remaining.
"It just shows that our league has a little bit of respect," Rose said of the high rankings of both teams.
HARTSOCK CRIES NO FOUL: Cougar forward Noah Hartsock said his last-second drive to the hoop Saturday in hopes of sending the game to overtime that was swatted away by New Mexico's Darrington Hobson was a clean block.
"He got there with great timing, and he had a great block," Hartsock said. "He made a great play. ... The whole game was physical and I wouldn't call that play a foul."
Hartsock said once he turned around with the ball and saw a path to the hoop, his intention was to dunk it.
"I knew there wasn't very much time on the clock, so it was just try to go as hard as I could to the rim," he said.
HAWS ADDS TO BYU'S DEAD-EYE FROM THE LINE: Earlier this season Jimmer Fredette set a BYU record by making 39 consecutive free throws. Freshman Tyler Haws has currently hit 28 consecutive free throws, and has made 90-of-100 on the season. Fredette, who missed five free throws in a win last week against San Diego State, is now making 87.8 percent of his free throws — hitting 158-of-180.
CONFERENCE RANKINGS: The Cougars lead the MWC in scoring offense (80.1 ppg), scoring margin (14.1), 3-point field goal percentage (40.1), free throw percentage (76.5), turnover margin (4.4), steals (7.9), assists/turnover ratio (1.5), defensive rebounds (27.8) and 3-point field goals made (8.2 pg). They are second in the conference in rebounding offense, field goal percentage defense, 3-point field goal percentage, assists and defensive rebound percentage. They're third in field goal percentage.
Fredette leads the league in scoring (20.6 ppg), 3-point field goal percentage (51.4) and 3-point field goals (38) made. Haws is tops in free-throw percentage (90 percent) and Jackson Emery leads the conference in steals (2.8 pg).