Dempster originally had a gastrointestinal disorder over the weekend. Hip and back soreness have manifested since then, and he's also been dealing with general lethargy. He was in the hospital overnight Saturday, getting tests and intravenous fluids.
"[Dempster] played catch [Wednesday] and felt pretty good," Cubs manager Mike Quade said. "Let's see how he comes in [Thursday] if he can toe the mound [Thursday] and pitch off the mound [Thursday]."
Generally a starting pitcher throws 30-40 pitches in a side session under the supervision of the pitching coach two days before a start.
"If that does happen we will look at the Pittsburgh series [Saturday]," Quade said. "And then we will see where we're at. He wants to pitch badly. He felt pretty good playing catch [Wednesday] but the exertion will be a little more even if it's a soft side session."
Carlos Zambrano, who was put on the DL on July 1 with lower back soreness, was scheduled to throw his first side session Wednesday at Wrigley Field. With all of the team's personnel in Washington, Quade's brother Scott was scheduled to catch Zambrano.
"We will go from there and see how he comes out of [the side session]," Quade said. "[Cubs trainer] Mark O'Neil and his guys are monitoring that. Then after that I don't know what the game plan is, but if he had a healthy side session [Wednesday] all systems are go to throw a simulated game or do something to get him ready to come back off the break and be ready to go."
Zambrano, who is going to Guatemala during the All-Star break on personal business, is eligible to come off the DL on July 16.
If Dempster goes on the DL or is just held out of his start on Saturday, Casey Coleman could take his spot. Coleman is on the same pitching day at Triple-A Iowa as Dempster. He took Dempster's spot on Monday and allowed two earned runs in 5 1/3 innings during the Cubs' 5-4 loss to the Washington Nationals.
If Dempster does go on the DL it would be retroactive to his last start, allowing him to come off the DL right after the All-Star break.
Bruce Levine covers the Cubs for ESPNChicago.com and ESPN 1000.