Christian McCaffrey will not be activated for Thursday night’s game in Seattle against the Seahawks, league sources told ESPN on Saturday, even though the 49ers star running back is eligible to return.

The bigger question continues to be when McCaffrey, who has been on injured reserve since Week 2 with calf and Achilles tendinitis issues, will be able to return.

McCaffrey’s return depends on how he fares in practice, but for now, there is some mild encouragement because the three-time Pro Bowler’s calf and Achilles issues did not flare up after on-field work this week — his first on-field work since being placed on IR, according to league sources.

Although McCaffrey has been dealing with bilateral Achilles tendinitis, his issue is concentrated to one of his legs — and the other is faring better, according to sources. The bilateral Achilles tendinitis is not considered a concern, according to sources, who told ESPN that McCaffrey is focused on avoiding setbacks as he continues to ramp up in a return to play.

If his progress continues without any setbacks, McCaffrey could return Oct. 20 for a Super Bowl rematch against the Chiefs, according to league sources.

There also is a chance McCaffrey could return for an Oct. 27 game against the Cowboys, according to sources. But even more reasonably, the 49ers could opt to sit McCaffrey for both those games and then give him the bye week to continue to ramp up for their next game at Tampa Bay on Nov. 10.

The Niners do not know which of those weeks is the most realistic return date, but they do know that McCaffrey hasn’t suffered any recent setbacks.

McCaffrey went to Germany last month to consult with a specialist, hoping to resolve the issue that has bothered him since early in training camp. The two-time All Pro missed four weeks of practice before returning to the field on a limited basis before the season opener Sept. 9 against the Jets. He was a late scratch for that game and then went on IR on Sept. 14, two days after experiencing pain in the Achilles tendon following a practice.

McCaffrey, 28, led the NFL last season with 2,023 yards from scrimmage and was tied for the league lead with 21 touchdowns, winning AP Offensive Player of the Year.

Information from The Associated Press was used in this report.