The International Paralympic Committee (IPC) issued a blanket ban on all Russian competitors at last year's Rio Summer Paralympics.
IPC president Philip Craven on Monday said Russia also faced the very real possibility of being excluded from London this year and the Winter Games in Pyeongchang as well.
Russia were suspended by the IPC in August following revelations of widespread state-sponsored doping uncovered in a report by Richard McLaren on behalf of the World Anti-Doping Agency (WADA), which also saw the country's track and field team banned from the 2016 Rio Olympics.
The IPC established a taskforce to monitor and assist the Russian Paralympic Committee (RPC) in a process of reforming.
But while encouraged by aspects of the RPC's "progress", Craven told reporters in London: "With 291 days to go until Pyeongchang 2018, there is not a moment to waste.
"The IPC taskforce will next update the IPC governing board in September and if the obligations have not been fully met by then it will be very difficult for the (Russian team) to have its suspension lifted in time to enter its athletes into the Paralympic Winter Games."
The veteran British administrator added: "Clearly, with this timeline in mind, unless something dramatic changes in the next few weeks, the Russian Paralympic Committee will not be able to enter its athletes into the London 2017 World Para Athletics Championships.
"At the moment there are a lot of good plans with timelines on paper but we now need to see plans in action and delivering concrete results."
The World Para Athletics Championships take place at London's Olympic Stadium July 14-23.
But with the IPC's deadline for London entries June 9, there is little time for Russia to convince the IPC it has met the criteria for a return.
The IAAF, which governs track and field, has paved the way for individually vetted Russians to compete as neutrals.
But IPC spokesman Craig Spence ruled out a similar arrangement in Paralympic competitions, saying they could only accept entries from member nations.
Meanwhile taskforce chairman Andy Parkinson, a former head of UK Anti-Doping, said that were Russian competitors to return now it would "jeopardise the integrity" of Para sport.
"The evidence is quite clear: the problems identified were far beyond individual athlete violations and an anti-doping system that was not strong enough to catch those athletes," Parkinson said.
"Instead, the system itself and the institutions that support this system were operating with the objective of circumventing the very rules the system was responsible to uphold."
Russia reacted coolly to Craven's remarks.
Mikhail Terentiev, a member of the RPC executive committee, believes the problem can only be resolved after Craven's 16-year reign comes to an end and a new president is elected in Abu Dhabi in early September.
"Unfortunately we haven't been heard within the scope of the IPC taskforce work," Terentiev told R-Sport agency.
"At some point we've lost the chance to discuss the problems of the Russian and international Paralympic Movement.
"(Philip) Craven put the situation into deadlock. And a positive decision (for Russia) can only be made after the election of the new IPC leadership."