"I wish him luck," Trump said when asked what message he had for Comey.
The former FBI director's testimony is expected to focus on the his interactions with Trump and a series of memos he kept about conversations he had with the President.
The comment came during a meeting with congressional leadership, including House Speaker Paul Ryan, Senate Majority Leader Mitch McConnell and Senate Majority Whip John Cornyn, where the group is slated to discuss Trump's stalled agenda on Capitol Hill.
Jared Kushner, a top White House aide and Trump's son-in-law, also attended the meeting. Trump joked during the gathering that his aide "has become much more famous than me."
Trump, through laughter, added: "I'm a little bit upset about that."
Kushner, who has found himself at the center of questions about the Trump campaign's ties to Russia
, was recently featured on the cover of TIME Magazine
The refrain is a common one for Trump, who said the same thing about Comey during a January reception for law enforcement at the White House.
"He's become more famous than me," the President joked before beckoning Comey over and giving him a warm handshake.
Comey's testimony, though still days away, has already garnered considerable attention and threatened to deepen the White House's problem of continued investigations.
Lawmakers tell CNN that Comey won't be constrained in recounting his conversations with Trump, but a Senate intelligence committee source also said that Comey is expected to abstain from discussing the ongoing federal Russia investigation.
Either way, Comey's testimony has consumed Washington's focus for the week, including inside the White House, despite their pledge to focus on infrastructure spending.