Robert Downey Jr was left looking uncomfortable after Oscars host Jimmy Kimmel appeared to allude to to the actor’s history with substance abuse.

The US host of the 96th Academy Awards took to the stage of the Dolby Theatre in Los Angeles on Sunday night, kicking off the ceremony with a customary monologue filled with jokes as the expense of those in the audience.

While addressing the success of Christopher Nolan’s epic Oppenheimer – which led the nominations with 13 nods – Kimmel, 56, said: “Congratulations to (Cillian Murphy’s) co-star Robert Downey Jr.

“This is the highest point of Robert Downey Jr’s career.”

Robert Downey Jr, left, and wife Susan Downey arrive at the Oscars (John Locher/AP)

After a pause, Kimmel added: “Well, one of the highest points,” before appearing to point towards his nose.

The camera then cut to Downey Jr, 58, who motioned that the joke was “on the nose” before he gestured for Kimmel to wrap it up.

Earlier in his career Downey Jr was arrested several times on charges related to drugs and went through treatment.

He also served time in prison for missing court-ordered drug tests.

After Kimmel’s gag, Downey’s co-star Emily Blunt could be seen reaching across to tap her friend’s shoulders as the actor appeared to look slightly uncomfortable.

The late-night comedian continued, saying: “Is that too on the nose or was that a drug motion you made?”

Another joke about whether the Iron Man star had an acceptance speech in his pocket or a “very rectangular penis” was also met with similar discomfort from the actor.

Downey J went on to win the best supporting actor prize at the ceremony, and thanked his wife Susan Downey for “loving him back to life”.