The Ivorian winger has featured in all four of Madrid's league games so far this season but has yet to complete even half an hour in a single appearance, totalling just 83 minutes from a possible 360.
Part of that is down to timing: Arda Güler has been in outstanding form on the right flank, raising the bar for anyone hoping to displace him, while Mourinho has made clear he wants to bring Diomande into the side gradually rather than thrust the most expensive signing in the club's history straight into the XI.
Diomande has featured for 26 minutes against Espanyol, replacing Güler, before a surprise six-minute cameo against Real Sociedad when he came on for Vinícius Júnior with Güler again starting. He then played 25 minutes against Málaga in place of a rested Brahim Díaz, and a further 26 against Betis last Friday, once more replacing Güler.
It amounts to 23 per cent of available minutes so far this season, without a goal or an assist to his name.
Mourinho addressed the situation directly in his press conference following the win over Málaga, making light of the fee involved while stressing the need for patience.
"Calm, he has to go little by little. He's played in three matches... 20 minutes, 15, 30... he's played in the three matches. He works well, a lot. He's an open, humble kid who wants to learn, to work," the Portuguese said.
"I can't look at the... how much was it, 120, 130? How much did we pay? I don't know! A hundred and something. But I can't look at that, I have to look at the young player with huge potential that he is, coming off a season of high-level football in the Bundesliga with Leipzig. Take it easy. Calm."
That patience may be tested sooner than expected, however, with Madrid facing Inter in the Champions League on Tuesday and both Güler and Bernardo Silva suspended for the fixture. With Eduardo Camavinga also banned and Aurélien Tchouameni and Thiago Alcântara still working their way back from injury, Federico Valverde cannot be shifted out wide to cover, leaving the right-wing berth to be filled by either Brahim or Diomande, barring a tactical surprise from Mourinho.
At just 19, Diomande is regarded internally as a player of rare talent, even if his start in Madrid has been deliberately understated. Sources close to the club describe a talent "of the kind you see rarely," while stressing there is no intention to place undue pressure on him before his time.
For now, the numbers remain modest, but as Mourinho put it, everything will come in time — perhaps starting against Inter.