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 European Tour "will have to adjust and adapt" if radical proposals to alter golf's majors schedule are implemented, says boss Keith Pelley.