But a complicated transfer window for the Magpies could be about to get even more challenging amid claims from the Brazilian's camp that the midfielder has indicated a desire to leave St James' Park and join the Premier League champions.
Arsenal are said to be willing to pay up to £60m for Bruno, but Newcastle remain adamant their captain is not for sale this summer.
There's been no contact from Arsenal or any other club, so despite the reports and speculation, Magpies sources say the club currently has no question to answer.
But fresh reports tonight claim Arsenal are stepping up their pursuit of Bruno, who is currently on a break following Brazil's exit from the World Cup.
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Newcastle have already lost Anthony Gordon and Sandro Tonali this summer, but there'd long been indications that both of those players felt it was the time to move on, so those exits, while clearly not ideal, were by no means bolts from the blue.
The Magpies have already landed Bazoumana Toure as a replacement for Gordon, Sean Steur is on the verge of joining from Ajax and the pursuit of Switzerland international Johan Manzambi is ongoing. Manzambi is said to want to put his club future on hold until the World Cup is over, with Switzerland currently preparing for a quarter-final clash against Argentina.
But losing Guimaraes would be a hammer blow, both on the pitch and in the stands ahead of a pivotal season for the Magpies after last year's domestic disappointment.
Bruno still has two years left to run on his contract but it's understood Newcastle have the option of a 12-month extension, which would further strengthen their position.
Guimaraes is still coming to terms with Brazil's World Cup exit - the "saddest day of his life" - with Newcastle's captain missing a penalty in the last 16 defeat to Norway.
He posted on Instagram this week: "I've written and deleted this so many times I've lost count.
"I've always been here for the victories, so it's only fair that I step forward and face you all head-on in defeat. Football, which has given me everything I have, is now causing me the worst pain of my 28 years of life.
"Missing that penalty kick and being eliminated in the round-of-16 is tough.
"It's agonizing, it hurts a lot but it will be just another obstacle to overcome. I've been through so much that only I know...I'm certain that, no matter how bad I'm feeling right now, it will all pass.
"The craziest part of it all was coming home after the saddest day of my life, and the first thing my kids said when I woke up was, "Daddy, let's play football?" And that's when I realised that, regardless of whether the days are good or bad, football will always be my great love."