Roy has played all 11 of England's white-ball internationals during an intense month of limited-overs action but has been well short of his buccaneering best.
Since hitting his 10th ODI century against a modest Netherlands team in Amstelveen in June, Roy has laboured against India and the Proteas with a top score of 43 and a visible lack of fluency at the crease.
With one half-century in his last 13 T20s, and Lancashire's Phil Salt waiting in the wings, the 32-year-old is in need of a score but Jordan insists his team-mates have full faith that a big one is just around the corner.
Sunday's winner-takes-all clash at the Ageas Bowl, in which England need a victory to avoid a winless first summer under Jos Buttler's captaincy, would be the ideal time.
"Jason is definitely the type of character to come through it," said Jordan, who captained Roy for Surrey in this season's Vitality Blast.
"We all go through it as cricketers, we all go through little patches, but we in the dressing room back him 250 per cent because we know that when he's on song he's a real match winner. Don't be surprised if he comes good on Sunday.
"T20 cricket is one of those things. Sometimes you can be hitting the ball well (and struggling) or not well and still getting runs. He will debrief his game with the coaches but as a character he will be back."
Jordan speaks from experience when it comes to conquering a dip in form. Last November in Abu Dhabi he faltered in the semi-final of the T20 World Cup, shipping 23 runs in the 17th over against New Zealand.
England had been favourites when he took the ball and were on their way out of the tournament by the time Jimmy Neesham had finished with him. At the time, it looked like his status as one of the side's most reliable death bowlers might have been fatally compromised, but in recent days he has excelled in the role.
He closed out victory in Bristol by allowing just three runs in the 18th over and five in the 20th, then followed up in Cardiff by restricting the tourists to just four in the concluding over - denying Rilee Rossouw a seemingly inevitable hundred in the process.
With his top pace back up to 90mph and a bankable yorker, he once more looks likely to be England's closer when they make another tilt at the T20 title in Australia this autumn.
"So far so good, it was nice to close out the first game in a win," he said.
"I haven't been watching the speed gun too much, but it's nice to be touching 90mph. I'm trying to bowl a higher percentage of yorkers, not to give too much away, because it's one of those balls that's hard even if the batter knows it's coming. I try to focus on my execution and live with the end results.
"I had a decent stint with Surrey and tried to take that momentum back into international cricket. Being involved in captaincy took a lot off me personally."