Barcelona may have to prepare for El Clasico without superstar forward Lionel Messi. The Argentine’s recovery from a left knee ligament injury was expected to coincide with a return to the pitch against archrival Real Madrid on Nov. 21 at the Santiago Bernabeu, but the 28-year-old has yet to return to training, leaving doubt over his availability for the critical La Liga matchup.

Messi originally suffered the injury in the opening minutes of a 2-0 domestic victory over Las Palmas on Sept. 26, and reports later indicated he would miss six-to-eight weeks with a knock to his internal collateral ligament but still come back in time to challenge Cristiano Ronaldo and Los Blancos.

Yet reports Messi’s rehabilitation has fallen behind schedule, and unless he can fully practice prior to the season's first Clasico he’s likely to sit out a little while longer.

"He will only be able to be on the pitch if he takes part in some entire training sessions,” former head of Barcelona medical services Jordi Ardevol told Goal. “We need to be careful and if he is not accomplishing the minimum [medical] requests, the best thing to do is not play because he could easily relapse on his injury."

Originally holding out hope to come back in time to participate in Argentina’s fixtures later this month, Messi is also expected to sit out international duties.

One source also told ESPN Deportes that “short of a miracle” Messi probably won’t see the pitch again until early December. The prolific scorer and deft dribbler is reportedly one week behind his original recovery timetable and he’s experiencing pain in the knee while running.

With Neymar and Luis Suarez successfully expanding their roles, the Catalans have largely steadied the ship on both the domestic and international fronts since Messi went down.

Other than the 2-1 loss to Sevilla, which was the first La Liga match without Messi this season, Barcelona remains undefeated in its last five matches and are in a dead heat with Madrid atop the domestic table with 24 points apiece. The Catalans are also in sole possession of first place in Champions League Group E after downing Bayer Leverkusen and BATE by a combined score of 4-1.

Much of the credit belongs to Neymar and Suarez and their ability to lead the attack in Messi’s absence. The Uruguayan’s netted seven goals in the last eight matches, including one in Saturday’s 2-0 victory over Getafe, while Neymar’s collected six goals and five assists in the last five matches.