The source close to ex-prime minister Francois Fillon said he would have lunch with Sarkozy after the former president returned early Monday from a conference in Shanghai.
Another source said the meeting had been planned several days ago, before talks to mediate the leadership fight collapsed on Sunday.
Called in to mediate the dispute, party heavyweight Alain Juppe threw in the towel after only 45 minutes of talks between Fillon and his rival for the leadership, party secretary general Jean-Francois Cope, late Sunday.
Fillon, 58, and Cope, 48, have traded accusations of fraud and ballot-rigging since last Sunday's party vote ended with Cope ahead by a handful of votes.
Fillon said Cope was solely to blame for the failure of the mediation efforts and said he would turn to the courts to resolve the dispute.
The crisis has thrown the UMP into turmoil and raised the spectre of an unprecedented split on the right.