BOSTON -- Boston Celtics big man Al Horford missed his eighth straight game Wednesday. It has been 17 days since Horford was concussed when a teammate inadvertently struck him during a practice on Halloween, and the Celtics remain uncertain of when he'll return to game action.

The fact that Horford signed a monster contract this summer (four years, $113 million) combined with Boston's uneven play without him has left many Celtics fans restless for his return. What's prudent to remember is Horford's injury history suggests a player who exercises great caution with his health before returning to the floor.

Celtics fans need only rewind to the 2011-12 season. Horford tore his left pectoral muscle and underwent surgery in mid-January. After three months of rehab, he initially declared himself out for the opening round of the postseason, before being given the OK by his operating doctor to return as early as Atlanta's regular-season finale. Horford still waited an additional 10 days, until Game 4 of the Eastern Conference first-round playoff series against the Celtics, to make his postseason debut (this after the Hawks lost an overtime thriller to fall behind 2-1 in the series).

When Horford tore his right pectoral muscle in late December 2013, he sat out the rest of the 2013-14 season. Despite being 10 months removed from the injury at the start of Atlanta's training camp in October 2014, he still elected to sit out the Hawks' first two preseason games. He then eased himself back with an 11-minute stint in Atlanta's third preseason tilt.

The encouraging news for Celtics fans: Horford went on to re-establish himself as an All-Star in that 2014-15 season, while appearing in 76 regular-season games. In fact, if you take away the two seasons in which he had pectoral injuries, Horford appeared in 93.7 percent of Atlanta's games in the other seven seasons.

Al Horford is using caution in recovering from injuries, preferring a complete recovery to a quick one. Ron Hoskins/NBAE via Getty Images

Both the 30-year-old Horford and coach Brad Stevens have been a bit cagey in discussing his injury, which can be expected to some degree because it's a head injury. That said, it has led to a lot of speculation about why Horford hasn't resumed game activity.

Horford traveled with the Celtics on a two-game road trip last week with the goal of playing but returned to Boston early. The Celtics were not scheduled to engage in full-throttle practice activity on either of their practice days this week.

On Tuesday, Horford suggested he isn't at liberty to discuss some of the symptoms he has endured or his progress through the league's return-to-activity protocol. "I'm just not where I want to be right now, but trying to work through it," he said.

Horford's sister, Anna, a vocal presence on social media, wrote Monday, "Better for Al to be out now [and] come back when he's 100 percent than come back too early [and] make things worse. Head injuries shouldn't be taken lightly."

That's a sentiment echoed by Horford's teammates, even if they are eager to get him back, particularly after Boston lost three in a row early in his absence. The Celtics have responded by winning three of their past four, but little has come easily for them (besides a romp over the Knicks). As Boston prepares to host the Golden State Warriors on Friday, you get the sense that the Celtics would love to have Horford on the court for a big national TV game against a Western Conference juggernaut. Even so, if Horford simply doesn't feel ready to play, he'll likely wait. To be fair, none of Boston's season goals can be accomplished in November.

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Part of the eagerness to have Horford back is that Boston has yet to see what it looks like with all its horses. At no point since the team convened for the start of training camp in late September has Boston had all of its players available.

Kelly Olynyk spent the summer rehabbing from shoulder surgery and missed the first seven games of the season. Marcus Smart sprained his ankle in the preseason finale and missed three games. Both players have elevated to starting roles recently due to injuries. Not only has Horford not played since Oct. 29, but fellow starter Jae Crowder has missed seven straight games because of an ankle injury.

Horford engaged in what Celtics coach Brad Stevens termed a "great" workout on Wednesday. Horford then went through another spirited session with assistant coach Jay Larranaga before Boston's win over the Dallas Mavericks on Wednesday night.

There is a chance that Boston could be at full strength against the Warriors if both Horford and Crowder respond well to activity on Thursday. But Stevens cautioned that it will take time for his team to fully re-congeal.

"I think it will still be an adjustment when we do [have everyone] just because those guys haven’t played in a while," Stevens said. "And knock on wood, we are together at some point, right? But we’ll see. Until then, we’ve got to still focus on playing well."

Stevens said he'll continue to plan as if Boston won't have its injured players and will happily audible if it does.

"I just kind of go through it with [the idea that] if they’re available, I’ll figure it out when the time comes," Stevens said. "But until then, I’m going unavailable in my own mind. I think that that’s the best way to do it. That’s the best way to organize your thoughts.

"If Al is able to play down the road later in the week, we’ll throw Al right in there, and I’ll adjust quickly."