Tim Legler says Rajon Rondo will give the Bulls a psychological lift if he plays in Game 5, but Rondo won't be able to beat the Celtics as a two-way player like he did in the first two games of the series. (1:49)

Chicago Bulls guard Rajon Rondo held a clandestine workout Tuesday night in Boston in an attempt to determine if he's healthy enough to return to the court for Wednesday's pivotal Game 5 against the Celtics, according to league sources.

Sources told ESPN that Rondo scheduled the private evening session to test his fractured right thumb and ailing right wrist in hopes of getting a better read on how feasible a comeback is after missing only two games.

Bulls point guard Rajon Rondo missed Games 3 and 4 with a fractured right thumb and ailing right wrist. Kent Smith/NBAE via Getty Images

‎"He wants to play bad," one source close to Rondo said Tuesday night. "As of right now, it's still tender and he's erring on the side of waiting until Game 6. But knowing him, he could change his mind in the morning and try to play."

A final determination on Rondo's availability for Game 5 is unlikely until closer to tipoff, sources said, but he has switched from a cast to a soft splint and did manage to participate in most of Tuesday's practice while protecting the injured hand.

Earlier Tuesday, Bulls coach Fred Hoiberg told reporters that Rondo was out for Game 5. But he didn't rule out the former All-Star's return during this series after Rondo was seen hoisting jumpers before the team's daytime practice.

Rondo suffered the injury in Game 2 and was expected to be in a hard cast for at least seven to 10 days. But Rondo, in the wake of the Bulls' two home defeats that evened the series at 2-2, showed up for Monday's practice without the cast.

Hoiberg continued to describe Rondo's return in this round as a "long shot" but also acknowledged that the 31-year-old was apt to try to do anything he could to come back after eighth-seeded Chicago squandered a 2-0 series lead.

"This is honestly the first time he's touched a basketball with that right hand," Hoiberg said of Tuesday's jumpers in front of the media. "We'll see. We'll see how it goes. He's going to continue to condition and do everything that he can. He was in the weight room yesterday getting a good session in there. It was his first time back in the weight room. He's just getting this whole process started."

After winning the first two games of the series in Boston, Chicago looked discombobulated without Rondo in Games 3 and 4. Backup point guards Jerian Grant and Michael Carter-Williams are shooting a combined 6-for-28 in the series and have turned the ball over nine times in the past two games alone.

Hoiberg is so desperate for a spark at point guard that he said he's planning to start little-used Isaiah Canaan in Game 5. It would be Canaan's first start of the season.

"It's so early in the process," Hoiberg said of Rondo's potential return. "Just watching him wince a little bit as the ball was coming to him makes me think it's a long shot; but if there's anybody that can do it, will try to fight through it, it's Rondo.

"Just because the competitor that he is and obviously wanting to get back out there. Doing everything that he can to put himself into position, knowing that it's obviously still a long shot for that to happen."

Rondo said after the injury that he considered himself a fast healer. The reason he was placed in the cast was to stabilize the wrist injury that he was dealing with late in the regular season. Hoiberg said Monday that the wrist tendon had "quieted down a little bit," enabling Rondo to remove the cast.

Rondo's potential return would provide a big morale boost for a Bulls team that was rocked by its two home losses. Rondo averaged 11.5 points, 10 assists, 8.5 rebounds and 3.5 steals in Chicago's two road victories to open the series.

"Obviously, that's huge," Bulls All-Star swingman Jimmy Butler said of Rondo's potential return. "We want that guy back, but I don't know if it will happen, if it won't happen; I can't tell you that.

"He's still out here shooting shots with his left hand from the corner. He just shot that one right-handed, actually, air-balled it. But we love him. He's our floor general out there. He knows everything. He knows every matchup, every position, and he's still helping from the bench. We really want him helping out there from the floor."‎

ESPN's Nick Friedell contributed to this report.

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