Howe's own position has come into focus in the last 24 hours, following widespread reports that he's preparing to step down, just a few weeks before the start of the 2026/27 Premier League season.
Newcastle fans are concerned captain Guimaraes will follow him through the St. James' Park exit door as Arsenal prepare a formal transfer offer.
The 28-year-old is due back in preseason training in the coming days, and will fly out to Spain with the rest of the squad for an intense preparatory camp at the start of August, with the Gunners ready to offer around £75M for the Brazil international.
Howe spoke after Newcastle's 4-1 friendly loss to Bristol City and admitted Guimaraes could be on his way out.
"We want to keep our best players. They're so valuable, and as I've said numerous times, there aren't many of them, so to get them and develop them is difficult.
"Bruno's very much in that category, he's an outstanding player.
"Assurances - I don't think you can push too hard for those. I've said many times you want players that are committed. Bruno's always been committed here. His training performances, his game performances, have been outstanding.
"Every time he's worn the shirt, he's played with the fans by his side. I'd love to see that continue."