Howe says he has had "really good conversations" with Guimaraes but could offer no guarantees over his captain's future, speaking after Newcastle were held to a 1-1 draw by National League neighbours Gateshead in their second pre-season friendly of the summer.
Arsenal are reported to be preparing a £70m offer for the Brazil international, and Howe stopped short of ruling out a departure.
"I've had some really good conversations with him before the World Cup, during the World Cup and after the World Cup," Howe said. "What we speak about has to remain private, but he's just a great player, a great person.
"I don't know what's going to happen with Bruno's future. That's for other people to speculate about. They are conversations that I'm not part of."
Guimaraes, Newcastle's Player of the Year after scoring nine Premier League goals and eight assists despite missing 15 games through injury, is due back at the club on Friday before flying out with the squad for a training camp in Spain. Howe pushed back on comparisons with Liverpool's pursuit of Alexander Isak last summer.
"Bruno is the captain of our football club. He's been an unbelievable player and person all through the time we have worked together," he said. "We absolutely love him and, of course, everyone will want him to stay."
On the pitch at Gateshead International Stadium, Luke Supyk gave the hosts a first-half lead, prodding home after Billy Chadwick's deflected free-kick fell into his path. Newcastle levelled late on when Lewis Hall's cutback, following a through ball from Jacob Ramsey, cannoned in off Ben Williams for an own goal. A crowd of more than 7,000 observed a minute's silence for Kevin Keegan before kick-off, while Fabian Schar made his first appearance since January's ankle injury and summer signing Sean Steur impressed on his debut in midfield.
Howe praised Steur, who arrived from Ajax this summer as part of a shift towards signing players aged 20 and under.
"He played really well today. He can be really pleased with his performance and first showing in Newcastle colours," Howe said. Willem Weijs, who coached Steur at Jong Ajax, described him as "one of the highest-rated" players to come through the academy.
"He's outstanding in his first touches and creating options when playing a possession game. He's good at scanning; really comfortable on the ball; really good in tight spaces," Weijs said.
"He's a typical Dutch-type midfield player, but he should focus on his defensive part. He should compete better in the duels, spending much more time in the gym. I know he's working on that, but he has to improve."
Newcastle's midfield rebuild follows Sandro Tonali's £100m move to Tottenham, with Steur joined by new arrivals Aladji Bamba, Ewen Jaouen and Bazoumana Toure. Howe acknowledged the project requires patience given the club has already lost Isak, Tonali and Anthony Gordon over the past year.
"We all need to be very supportive to the players that have come in," he said. "I don't think we can put too much pressure on them. It's part of my job to try and take the pressure off them and allow them to develop and to enjoy their time here."
Newcastle continue their pre-season preparations at Bristol City on Wednesday.
Newcastle United: Pope (Jaouen 69), Hall (Salia 82), Schar (Pivas 60), Barnes (Park 77), Steur, J. Murphy (Sanusi 77), Willock (Charlton 82), A. Murphy, Ramsey (Munda 82), Shahar (Miley 69), Neave (Ferreira 69). Subs not used: Gillespie, Harris, Craggs, Finneran.