The 28-year-old Brazil international's stance has pushed Arsenal into taking negotiations up a level. Rather than working solely through intermediaries, as had been the case until now, the Gunners have opened direct talks with Newcastle United over a deal, reports The Sun.
Newcastle have consistently maintained that their midfielder is not for sale, and that stance has not softened despite Guimaraes making his preference known. Arsenal, working through representatives, had previously signalled a willingness to pay £60million, but the Magpies are digging in and want considerably more before they will even entertain a sale.
That gap in valuation could prove decisive. Some reports in recent weeks have suggested Newcastle's true asking price sits closer to £100million, with the north London club having been given hope of a cut-price deal that may not materialise.
Arsenal's pursuit of Guimaraes comes off the back of a frustrating few weeks in the transfer market. They were priced out of a move for Morgan Rogers, who instead completed a British-record £117million switch to Chelsea after Aston Villa accepted the offer. The Gunners were unwilling to match Villa's valuation and shifted their focus elsewhere.
A separate move for Mateus Fernandes also fell through on cost grounds, with Arsenal judging his £85million fee too rich before the midfielder joined Tottenham instead. Bournemouth's Alex Scott was also considered, but the Cherries are refusing to sell despite the England international turning down a new contract at the Vitality Stadium this week.
With midfield reinforcements proving hard to find, Guimaraes has become Arsenal's priority target, even if it means a prolonged standoff with Newcastle over a fee before pre-season begins in earnest.
Guimaraes joined Newcastle from Lyon and has since captained the club, becoming one of the Premier League's most consistent midfielders. He still has two years left on his current deal, with the option of a further year, meaning Newcastle are under no financial pressure to sell unless an acceptable offer arrives.
Eddie Howe will be desperate to keep his captain and avoid repeating last summer's saga involving Alexander Isak, whose stand-off eventually ended in a big-money exit to Liverpool.