World number one Rory McIlroy has offered another clue which suggests he plans to return from injury to defend his USPGA Championship title next week.

McIlroy suffered a “total rupture” of ligaments in his left ankle during a game of football with friends on July 4, ruling him out of the Scottish Open and the defence of his Open and WGC-Bridgestone Invitational titles.

The 26-year-old has yet to say whether he will be able to compete at Whistling Straits next week, but on Friday posted a picture on social media which appeared to show the inside of a private plane along with various emojis depicting a US flag, a thumbs-up symbol and a golf flag.

The on-board video screen suggests McIlroy was departing from Faro in Portugal, where the four-time major winner is understood to have been practising and the location for Thursday’s video of him hitting a driver on the range.

On Wednesday McIlroy posted a video on his Instagram account in which he was seen balancing on his left leg and twisting and throwing a gym ball to mimic the actions of the golf swing.

Alongside the short video clip, McIlroy wrote: “Working hard every day to come back stronger #dontmindthegrind.”

He has also shared photographs of his ankle from four and three weeks ago, saying: “I’ve come a long way since.”

McIlroy will be replaced as world number one by Masters and US Open champion Jordan Spieth if the 22-year-old American can win his first World Golf Championship title at Firestone Country Club this week.

It was at the same event that McIlroy overturned a three-shot deficit to Ryder Cup team-mate Sergio Garcia in the final round 12 months ago to move back to the top of the rankings.

McIlroy’s last competitive round was a closing 66 in the US Open at Chambers Bay on June 21.

The USPGA gets under way on August 13. The groupings for the opening round will be revealed on Friday evening.