At least 132 students and nine staff members are reported to have died when Taliban gunmen broke into a school and opened fire in the bloodiest massacre Pakistan has seen for years.
"It is a national tragedy and a barbaric act," Khan told the National newspaper. "Playing the match is going to be very difficult. How do you play a match when your spirit is not in the game?"
The 37-year-old, who has featured in 96 Tests and 257 one-dayers for his country, likened the situation to the one Australia experienced last month when batsman Phillip Hughes died after being struck on the head by a bouncer.
"When Phil Hughes died it shocked every one of us and we postponed a day's play in the test match against New Zealand," he said.
Pakistan lead the five-match series 2-1 after winning the first match in Dubai and the third in Sharjah.
The Black Caps won the second match, also in Sharjah, and have their sights set on levelling the series in tonight's must-win encounter.
New Zealand batsman Martin Guptill accepts he and fellow opener Anton Devcich need to lift their efforts, after failing to provide their side with any momentum in Monday's humiliating 147-run defeat.
"We just didn't get things right," Guptill said. "We didn't have a platform to be able to launch from towards the end of the innings like Pakistan did and that's the key in chasing big totals and setting big totals, is having a platform from the top order, and we weren't able to do that the other night.
"But we're going to be working on that at training today to be able to go out and give the platform that we need to launch at the end of an innings."
The 28-year-old's stay at the crease last just 19 deliveries but Guptill is confident he can turn things around quickly.
"I'm feeling good at the moment. The other night didn't go to plan for me but I'll be much better. It [has] put me in good stead for the next game, having that innings under my belt. I'm just going to go out at training today and just bat and try and get a bit of rhythm back into my batting and then go out tomorrow and do my best."
Despite their inconsistent form, Guptill insists the feeling in the Black Caps' camp remains positive.
"The spirits are still high. We've got a chance to come back and win three-two so there's still a lot of excitement in the camp at the moment.
"There's a lot of guys with a lot to prove and we're all excited to get out there tomorrow and show that we can do it. We know that we can do it so it's all about just playing to the best of our abilities.
"We've got two more games to go out and prove we can do it and we know we can do it so tomorrow and Friday's about going out and showcasing our skills."
The players are to observe a minute's silence before the match and will wear black armbands.
