A revamp of the calendar is under consideration with the 2019 US PGA Championship potentially moving to May.
That would mean the US major being played in the same month as the European Tour's BMW PGA Championship, which starts at Wentworth on Thursday.
This could have long-term implications for the quality of the field.
US officials are considering the date shift to try to prevent the climax of the PGA Tour season being overshadowed by the beginning of the American Football season.
They want to free up the month of August for the FedEx Cup play-offs to be completed before the start of the NFL campaign which dominates American sports viewing from September onwards.
Pelley accepts there could be serious knock-on effects for his tour.
"Right now we are looking at our 2018 schedule but at the same time 2019 and 2020 are in our discussions daily as well," he told BBC Sport.
"If there are changes that happen in the US with the majors then we are going to have to adjust and adapt."
Pelley added that next year's European Tour schedule will follow similar lines to the current timetable, but he cannot guarantee this will remain the case in following years.
"It will depend on what they do in 2019," he said. "The PGA of America says they're going to determine whether the PGA Championship is moved to May by the end of August this year.
"If that's the case we are going to have to look at everything.  We have plans right now but there is no doubt that if those changes happen, the 2019 and 2020 schedule will be considerably different to 2018."

The race - the final round of the FIA World Rally Championship (WRC) - starts in Llandudno, Conwy county, on 12 November and finishes in Deeside, Flintshire, on 15 November.
Along the way, it will take in towns and villages in Powys, Gwynedd and Denbighshire.
The rally is thought to be worth Â£10m annually to the Welsh economy.
Councillor Avril York, Powys council's cabinet member for regeneration, said north and mid Wales was an ideal location for the event.
"The area lends itself so well to rallying as we have the forests, mountains and magnificent scenery," she added.
"This prestigious event brings so many benefits to the area."
The line-up includes the world's top stars including the newly-crowned 2015 World Rally Champion Sebastien Ogier and Welsh driver Elfyn Evans.
The final round of the FIA World Rally Championship (WRC), the race will receive Â£4.5m from the Welsh government over three years.

Salon Privé has relocated from London to Blenheim Palace for its 10th anniversary, and the three-day event culminates with a "public day" on Saturday.
Co-founder David Bagley described the cars on display as "amazing".
They include the Aston Martin DB10, only 10 of which were made, soon to be seen in James Bond movie Spectre.
However, 007's car can only be seen by premium ticket holders.
Mr Bagley said: "It's the first time we've had a public day.
"For me it's a real opportunity for dads and their lads. All kids love cars.
"The cars we bring here, half of them will have never been seen before. There's going to be a lot of noise, a lot of atmosphere."
There are supercar and hypercar models on show by Ferrari, Koenigsegg, Pagani, McLaren, Zenvo, some of which are worth in excess of £1.5m.
The top tier hypercar category is one increasingly used by car aficionados, and refers to the most expensive and highest-performing supercars.
The event is usually targeted at private buyers, collectors and enthusiasts, but "outgrew" its original locations in Hurlingham and Syon Park.
Mr Bagley added: "As beautiful as they were, Blenheim now offers us an opportunity to create a lovely private event on the south lawn and a public event on the Great Court."
The public part of the show will include a grand parade of more than 60 supercars from 1975 to the present day.
Jamie Spencer-Churchill, the 12th Duke of Marlborough, said it was an honour for the palace to be involved.
"My wife, and son The Marquess of Blandford, and I are personally looking forward to the event as big motor enthusiasts," he added.
The European Tour "will have to adjust and adapt" if radical proposals to alter golf's majors schedule are implemented, says boss Keith Pelley.
[NEXT_CONCEPT]
The route has been confirmed for the Wales Rally GB, with 78 cars competing in the international race.
[NEXT_CONCEPT]
A prestigious motor show for rare and luxury cars is to open to the general public for the first time.