Zaheer, 25, has not played a competitive game since he was sidelined in December because of a hamstring injury during the Test series in Australia.
"Definitely there will be extra pressure because I am coming out of injuries and have not played matches for a few months," he told reporters on Monday.
"I need to give that extra bit now and play harder."
India, set to play their first Test tour of Pakistan in 14 years, leave on Wednesday to play five one-dayers and three Tests. The one-day series starts in Karachi on Saturday.
Zaheer took five wickets in Australia's first innings in the opening Brisbane Test as India drew the rain-hit game.
India confounded critics by going on to draw the series 1-1, but Zaheer, who suffered the injury in Brisbane, made a feeble return for the third Test in Melbourne before he was ruled out for the remainder of the tour.
Injuries have ruled out India's main spinners Anil Kumble (shoulder) and Harbhajan Singh (finger surgery) plus pace bowler Ajit Agarkar (shin) for the Pakistan one-dayers.
Fellow left-arm paceman Ashish Nehra had to prove his match fitness in the domestic Duleep Trophy event after struggling in Australia on his comeback after a long layoff following ankle surgery.
Zaheer said he was pleased after bowling in a practice game on Monday. "I bowled with my full effort. I am feeling good and I am already gaining rhythm. It's only going to get better."
He said he had received useful tips from ex-India captain Kapil Dev and former Australia pace bowler Dennis Lillee.
"I am working on Lillee's tips and hope it will help me perform better," he said.
Lillee advised Zaheer to curb his delivery stride to reduce the risk of leg injuries he has suffered in the last three years.
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