The Ireland centre - who has swapped Guinness PRO12 reigning champions Connacht for Leinster over the summer - sustained the injury in last month's second Test against South Africa.
Leinster's season starts on September 2 against Benetton Treviso and Henshaw believes he may be out of action for at least the first six weeks of the campaign, pencilling in a return ahead of the Champions Cup games in October.
"It's not an ideal start for me," he told the Irish Examiner. "I was pretty shocked to hear when it happened.
"It's one of my first big enough lower limb injuries. It's not ideal. Starting with a new club you want to make a massive impact from the get go so it's not a good start for me. The only thing I can do is do the best I can to recover and get back.
"To be optimistic I'd be aiming for before [Ireland's November game against the All Blacks], maybe for the European games in the Champions Cup. But to be honest I can't say."
Henshaw was one of the stars for Connacht as they completed their underdog story by overcoming four-time PRO12 champions Leinster back in May.
And while the 23-year-old left Connacht with a heavy heart, he believes working with the likes of Jonathan Sexton on a daily basis will help raise his game.
"Even just for me, the change needed to come," added Henshaw. "I've been there a long time. I needed the change for myself as well and to go and get experience off guys who have got to that next level, for example Jonny Sexton, Jamie Heaslip, guys who have played in the Lions team.
"Obviously Connacht did a lot for me over the years as well, skills-wise and development-wise as well, but hopefully now I can get to that next level. I love a challenge, I want to keep improving my game.
"I'll never settle to not improve my game so I think that's one of the reasons. I need to be pushed by other guys, that's one of the things that you need to improve."
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