Imran Khan is recovering in hospital after being shot in the leg on Thursday at a protest march in Wazirabad.
One person was killed and at least 10 injured in the attack on his convoy.
But Mr Khan is in a stable condition, his team say, and could potentially be discharged in the coming days.
Following Thursday's shooting, his party - the Pakistan Tehreek-e-Insaf (PTI) - called for nationwide protests after Friday prayers.
Schools have been closed in the capital, Islamabad.
President Arif Alvi calls it a "heinous assassination attempt".
Prime Minister Shehbaz Sharif orders an immediate investigation.