Dick Gomez shared images of himself at the event on his Instagram story, posing alongside agent Nojan Bedroud of Sport Invest and tagging Guimaraes' representatives Giuliano Bertolucci and Alexis Malavolta, according to Newcastle World.
TransferRoom's Madrid gathering, dubbed the transfer equivalent of speed dating, brings together more than 300 club owners, sporting directors, chief executives, loan managers and agents from over 40 countries for four days of rapid-fire meetings, as reported by Mail Online.
One Premier League executive described the format to the outlet: "The room is set out like a GCSE exam. You have about 16 slots per day, and you go through the attendees and request to meet them, the system fills up all of your spots as you accept or are accepted.
"All the tables are numbered, and you get your own programme and each meeting is on a different table. There's a giant green digital clock usually hanging on the wall that counts down and when the bell rings three times, it's time to move on. Ding, ding, ding. Off you pop to the next table, the next meeting.
"There's two packages. Basic membership costs about £20,000 and the full is about £35,000. The difference is what you have access to. That means access to pitch as many players as you want, reply to as many pitches as you want and access to add-on tools, getting deeper insight to things like player statistics."
Gomez, who co-owns the Next Gen Brazil agency with Malavolta, was there representing the firm rather than in any official capacity for his son, though the timing will inevitably add to speculation.
Guimaraes has two years left on his contract at St James' Park, with the club holding an option to extend by a further year. Arsenal had a formal offer for the Newcastle United captain rejected on Monday, and the Magpies are braced for an improved second bid, though it remains unclear whether it will meet the valuation United's decision-makers are demanding.
Guimaraes has since joined his team-mates at Newcastle's training camp in La Manga. Previous deals brokered at TransferRoom include Viktor Gyokeres' move to Sporting Lisbon and Antoine Semenyo's switch to Bournemouth.