France's Adrian Mannarino and Finn Jarkko Nieminen have been called up to replace France's Gael Monfils and Japan's Kel Nishikori who both withdrew from the Italian Masters before they were due to play later on Monday.
Monfils, the tenth seed, was forced to withdraw from the tournament citing illness, while Nishikori is suffering from kidney stones.
"I'm not 100%, I don't have any energy," said Monfils.
"I haven't felt well for a week. I've caught something, I'm not sure what. I'm going to have tests to see what will happen."
Lucky losers Mannarino and Nieminen were both beaten in Sunday's qualifiers.