The visit was listed on an updated weekly schedule for Tusk and gave no reason for it nor details of what would be discussed.
The visit was listed on an updated weekly schedule for Tusk and gave no reason for it nor details of what he would discuss with May.
An EU source told AFP separately that the visit forms part of the regular contacts Tusk and May agreed last week should take place during the negotiation process.
"May and Tusk agreed during their phone call on 28 March to establish a regular contact at the highest political level to create a channel for facilitating the Brexit process outside the day-to-day talks," the source said.
"The meeting is not part of the negotiations".
The announcement comes after the European Parliament on Wednesday overwhelmingly adopted tough "red lines" for the Brexit negotiations, saying the divorce terms must be agreed first before any talk of a new trade deal.
The parliament largely followed Tusk's own draft guidelines issued last week after May formally triggered the historic Brexit process.
The EU source said the meeting with May in London, expected around 1200 GMT, "will be a first opportunity for Tusk to explain his draft Brexit guidelines to be adopted on 29 April (by the remaining member states) as well as to discuss the next steps."
May has pressed hard for the divorce and trade deal talks to proceed in tandem but Brussels has repeatedly rebuffed her demands.
The 27 European Union states are due to sign off on Tusk's guidelines at a summit on April 29, paving the way for formal negotiations to begin at the and of May.
The EU wants a draft deal by October 2018 so that national leaders will have time to approve it before ratification by the European Parliament, most likely in early 2019.