He has had a high fever, lost about seven or eight pounds and had just enough energy to take some indoor batting practice on Friday.
"It has been ugly," said Drew, who was happy not to share more specifics. "Hopefully, I am on the mend."
Drew, who last played in a game on July 17, had enough energy to come off the bench and deliver a pinch-triple to right-center field with one out in the bottom of the ninth inning to drive in the winning run as the Washington Nationals beat the San Diego Padres 3-2 on Saturday night.
"He was super sick," Nationals manager Dusty Baker said of Drew. "He took another IV today. He took one yesterday and the day before."
It was the sixth walk-off win of the season for the first-place Nationals. Drew has six pinch-hits this year, including three homers and six RBIs.
"These guys battled back," said Drew, who watched part of the game on the bench. "These guys kept grinding (with) good at-bats. I was fortunate to get my 'A' swing off on a pitch I could drive" against Kevin Quakenbush.
Scherzer gave up four hits and two runs with 10 strikeouts and no walks in seven innings. Jackson, who played for the Nationals in 2012, yielded six hits and two runs in six innings.
"It feels good being able to come out and give the team a chance to win," Jackson said. "That's a great hitting team. It was a great outing. We just came up short."
It was the second start for Jackson with the Padres.
"He was good. He gave us an opportunity to win a baseball game. He threw the ball well," San Diego manager Andy Green said of Jackson.
Drew's hit scored Anthony Rendon, who singled to start the ninth for his second hit of the game.
The winning pitcher was Jonathan Papelbon (2-2), who worked a scoreless ninth, and Quackenbush (6-4) was saddled with the loss.
The first-place Nationals (58-40) won for just the second time in six games and the fourth-place Padres (42-56) have lost five of the last six. Washington is now 4-8 against the National League West.
Matt Kemp, who had two hits, smashed the first pitch in the top of the ninth for a double to left off Papelbon. After an intentional walk with two outs to Ryan Schimpf, pinch-hitter Brett Wallace popped out to the end the inning.
Washington's Shawn Kelley allowed a two-out triple to Travis Jankowski in the eighth but then fanned Wil Myers looking to end the threat. Myers, who got a day off Friday, struck out three times.
Schimpf, hitting .225 at game time, hit a long two-run homer off Scherzer in the second to give the Padres a 2-0 lead. His eighth homer of the year also scored Yangervis Solarte, who had singled to lead off the inning.
Scherzer has a habit of giving up homers to non-power hitters. The previous homer he allowed was July 4 at home to Martin Maldonado (three homers through Friday) of the Milwaukee Brewers.
Before that, he gave up two homers on June 24 at Milwaukee to Keon Broxton and Kirk Nieuwenhuis. That was the first homer of the year for Broxton and the fourth for Nieuwenhuis.
Washington's Daniel Murphy had a sacrifice fly in the third to drive in Ben Revere and cut the margin to 2-1 against Jackson.
Scherzer gave up just one run or fewer in seven of his previous eight starts. But the night belonged to Drew, who has played several infield spots this year in his first year in Washington.
"At the beginning of spring training, I didn't know. He didn't look as good as he does now," Baker said. "He has worked and he stays ready. We missed him the last few days. He has had a tremendous impact. He has done everything that we have asked of him."
NOTES: The game-time temperature was 94 degrees. ... ESPN reported that San Diego LF Melvin Upton Jr. could be traded to an American League East team, and FOX Sports said the Baltimore Orioles could be a landing spot. The Orioles had director of player personnel John Stockstill at Friday and Saturday's games in Washington. "We've chatted a little bit," Padres manager Andy Green said of Upton before Saturday's game. "Right now it's out in the distance. He's in the situation where multiple teams are after him, multiple teams are in the chase for a pennant, and winning the World Series. He's done all the things for people to take notice that he is the player from back in Tampa." Upton broke in with Tampa Bay in 2004 and also played for the team from 2006-12. Upton was hitting .259 with 16 home runs and 45 RBIs through Friday. Upton was in the starting lineup Saturday. ... San Diego RHP Andrew Cashner could also be dealt, according to several sources. "The way that Andrew has taken the ball out his last two starts have been his best two starts of the year, so it's (the rumors) clearly not impacting him," Green said. Cashner is 4-7 with a 4.79 ERA in 15 starts. ... Padres RHP Edwin Jackson, the Saturday starter, was 10-11 with a 4.03 ERA in 2012 for the Nationals. ... The Padres entered Saturday with a homer in 20 games in a row, a franchise record and the best streak in the National League this year. ... In Sunday's series finale, the Padres will start LHP Christian Friedrich (4-6, 4.55) against Washington rookie RHP Lucas Giolito (0-0, 4.70), who has made two big league starts.