Acrimony has grown between Vettel and Leclerc, with both having gone against the team's wishes to aid the other at different points in the season.
Vettel was left enraged when Leclerc failed to give him a slipstream in qualifying for the Italian Grand Prix and the German gained a measure of recompense when Leclerc towed him into the lead of the Russian Grand Prix, only to renege on a pre-race agreement to give his younger colleague P1 back.
Things came to a head in Brazil last weekend as the pair collided, leaving Ferrari with a first double DNF since Singapore 2017.
Team boss Mattia Binotto summoned both to Maranello to give their explanations, and Schumacher thinks Vettel is starting to move onto shaky ground.
"I believe there will be a difficult internal discussion, because Binotto slowly comes under pressure," he told Sky Deutschland.
"After all, Ferrari has other worries than its teammates constantly arguing. And they both have that responsibility. They are both old enough.
"I think it is serious enough that if it does not get better, if there are no clear commitments, then Ferrari might think about changing something.
"It will be very difficult for both of them but especially Sebastian. If they cannot find a solution, it is clear that the future is with Charles."
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