The Argentinian – a £40million signing from Manchester United last summer – has started just three of eight Premier League games since Rosenior’s appointment in January.
He was an unused substitute in three of those fixtures but he got his chance in Wednesday evening’s 4-1 win at Aston Villa with Pedro Neto suspended following his red card in Sunday’s 2-1 loss at Arsenal.
Rosenior revealed Garnacho, whose contract runs until 2032, recently suffered a “very difficult” event in his personal life and said the 21-year-old is “more than knocking on the door to start” games.
Than means the player could also line-up against Phil Parkinson’s Wrexham in the mouthwatering FA Cup fifth round tie when the Blues will aim to avoid a shock.
“Garna’s a top player,” said the head coach. “We’ve changed a little bit tactically since I’ve come in: I’ve wanted to dominate midfield areas, which has meant at times I’ve only played with one winger.
“But Garna’s an outstanding player and what I’ve really liked in this period is his reaction to not starting.
“He’s been training very, very well, and he’s definitely going to get his opportunities to play in the schedule we’ve got coming up.
“He’s a great kid. I know in the end his quality is going to show in a really consistent way.”
Chelsea’s midweek visit to Villa Park and cup clash at Wrexham is followed by a trip to France for the first leg of a Champions League last-16 showdown with holders Paris St Germain on Wednesday.
Neto’s one-match ban has further depleted Rosenior’s attacking options, with Estevao and Jamie Gittens working their way back from injury issues.
Despite his lack of top-flight action, Garnacho began FA Cup victories away to Charlton and Hull, while he scored twice coming off the bench in the first leg of the Blues’ League Cup semi-final defeat to Arsenal.
“You’ve got to take into account Garna is 21,” said Rosenior.
“He’s got huge ability, he’s got huge potential, and for any young player the biggest thing to be challenged on is your consistency level.
“But he’s showing really, really good signs in terms of not just in training but his engagement in meetings. He’s on a really, really good track.
“All Garna needs to do is keep working really hard because his ability is not in question.”