Buttler’s men wrapped up a 3-1 series victory over New Zealand with an emphatic 100-run victory in the Fourth ODI at Lord’s on Friday, their final game with a first-choice squad before they head to the subcontinent.
England named a provisional 15-man World Cup squad last month, but Harry Brook’s controversial omission has had debate over its final makeup - which does not have to be confirmed until September 28 - raging ever since.
Malan was seen as one of the players most at risk in the event of a late switch to bring in Brook, but silenced any questions over his place in empathic style with a player of the series display against the Black Caps, culminating in a fifth ODI century in the finale.
Asked whether Malan was now impossible to drop, Buttler said: “Yes.
“Every time he’s had his opportunity, not just this series but before, he’s been incredibly consistent, so absolutely, he’s played fantastically well, I thought it was a brilliant hundred.”
Instead it is opener Jason Roy who appears under pressure after missing all four matches of the New Zealand series with back spasms and, even if included in the squad, has likely lost his starting berth to Malan.
Even prior to his injury, Roy’s form had been a question and he could now be drafted into a second-string squad that will face Ireland in a three-match series from next week in a bid to prove his readiness.
“The biggest frustration is for him,” Buttler said. “He wants to be fit and playing, and affecting games of cricket for England.
“He’s been working really hard to be fit and available but we now have a few days where we can regroup - the coach, the captain, the selectors or whatever - and just work out exactly what we need to do moving forward.
“Obviously, we’ve had a few injury niggles as well around a few players so we can just gather a bit of information on that and then we can finalise the squad.
“It’s been an option all along to potentially add guys to the Ireland squad if needed so we’ll get a clearer picture from everyone now that this series has finished as to who needs what moving forward.”
Fast bowler Mark Wood was also missing throughout the New Zealand series as he recovers from the bruised heel he suffered up at the back end of the Ashes, while spinner Adil Rashid has not featured since picking up a calf issue in the First ODI.
England are being cautious with both players ahead of their World Cup opener against New Zealand on October 5, but Buttler admitted his frustration at being unable to field a full strength side at any point in the build-up.
“You don’t want to risk anything but at the same time you do want guys to play cricket,” he explained. “That’s our job to play cricket and we all want to play. Injuries are a really frustrating part of the game.
“[With] Adil, it’s fantastic when he’s available and bowling and building his confidence, especially when we’ve had six months not playing this format.
“In an ideal world, we’d have had a fully fit team to select from and give games to, but we haven’t been in that position, so that’s probably why we just need to take a day to work out exactly what we need to do before we do get on the plane to India.”
As well as the main 15-man squad, teams can name three travelling reserves to be brought in later in the seven-week tournament in the event of injury.
National selector Luke Wright said last month that England are hoping to make Jofra Archer one of theirs and excitement around the seamer’s potential involvement ramped up this week after he trained with the side for the first time since suffering a stress fracture of the elbow at the IPL in May. Buttler, however, urged caution over a player who has been plagued by injury over the last two years.
“We’ll see,” he said. “There’s a huge duty of care to him. He’s been out of the game for a while. He’s had his elbow and his back [injuries] and he’s still a young man who’s got a lot of cricket ahead of him.
“So there’s a massive duty of care to make sure that he’s fully fit for the rest of his career. It’s obviously exciting to see him in an England tracksuit and bowling and, even when he sort of looks like he’s going through the motions he creates a lot of speed. He’s a superstar and we’ll find out again more over time as to how he’s always travelling.”