Antonio Horta-Osório, chief executive of Santander UK, has been named as the new chief executive of Lloyds Banking Group.
He will fill the shoes of Eric Daniels at the lender which was bailed out by the UK taxpayer.
The resignation of Horta-Osorio would come ahead of a planned initial public offering of the Santander UK unit expected to raise about £4bn.
Some analysts said Horta-Osorio's loss could impact the planned flotation.
"This would appear poor timing for Santander, which might struggle to IPO Abbey with an unfamiliar chief executive. From a Lloyds perspective, we think he is a credible external appointment," Seymour Pierce analyst Bruce Packard said in a research note.