Christian McCaffrey’s Achilles tendinitis has kept him on the sidelines to begin the 2024 NFL season, a blow to the San Francisco 49ers and fantasy football managers alike.

The reigning Offensive Player of the Year, who is currently on injured reserve, is likely to miss months, not weeks, according to a doctor specializing in the type of treatment McCaffrey recently sought in Germany.

Dr. Kenton Fibel, the Anaheim Ducks’ medical director with expertise in orthobiologics — non-surgical treatments such as platelet-rich plasma injections — told the San Francisco Chronicle that McCaffrey’s trip to Germany suggests he will need a few months to get back on the field.

“I think it more suggests this is an injury that they think they are going to need something more to augment his healing that may require weeks or a couple months rather than a week or two,” Fibel told the Chronicle.

McCaffrey needed to visit a specialist in Germany because orthobiologics are not approved by the U.S. Food and Drug Administration — though North American sports leagues have no rules against them.

“This may be something where you realize the pathology is a little bit more serious and reserve a way to allow him to return this season, even if it does take a month or two with him needing a longer recovery,” Fibel said.

McCaffrey, 28, was placed on injured reserve after missing the Niners’ season opener. He is required to miss a minimum of four games while on IR and will be eligible to return for the Week 6 game against the host Seattle Seahawks Oct. 10, though the Chronicle report suggests he won’t be ready to play until around Thanksgiving or early December.

A three-time Pro Bowl selection and two-time first-team All-Pro, McCaffrey led the NFL with 1,459 rushing yards last season. He has four 1,000-yard rushing seasons and two 100-catch campaigns in 91 games (84 starts) for the Carolina Panthers (2017-22) and 49ers.