Sajid Javid, another heavyweight in the Tory leadership race, also appeared to rule out a Huawei 5G tie-up as he said: "I would not want any company, whichever country it's from, that has a high degree of control by a foreign government to have access to our very sensitive telecommunications network."
May overruled Cabinet ministers who warned her in a National Security Council meeting that allowing Huawei access to the UK's 5G infrastructure would compromise security.
Huawei is legally obliged to cooperate with the Chinese government if it demands access to information held by the company. May allowed Huawei to stay in the running for contracts to build "non-core" infrastructure, such as antennas, though a final decision on whether to freeze out the Chinese firm will now be taken by her successor.
Asked by Andrew Marr about Britain's final decision on whether to allow Huawei to bid for 5G contracts, Mr Johnson said: "I would caution, according to the president and people on the US side, to move much more slowly."
Huawei is not the only contentious topic that will come up during Mr Trump's visit.
Johnson suggested that Britain's "entire economy", including the health service, would be included in negotiations over a post-Brexit US-UK trade deal, but Matt Hancock, the Health Secretary, said that the NHS is "not for sale" and "will not be on the table in any future trade talks".
Trump is also prepared to challenge May over Britain's role in the investigation into his election campaign's ties to Russia when they meet in Downing Street tomorrow.
Trump's meetings with the Royal family could also be made awkward over his comments in interviews that the Duchess of Sussex was "nasty". Yesterday he claimed the remark had been "made up by the fake news media". The Duchess will not meet Trump.