England are 1-0 down after losing the second Test in Dubai and drawing the first in Abu Dhabi, so are seeking to level the series, as New Zealand did last year.
The Black Caps also used three spinners in Daniel Vettori, Mark Craig and Ish Sodhi to beat Pakistan by an innings, also in Sharjah for a 1-1 result.
Asked if England would play a third spinner in Samit Patel in place of Mark Wood who is rested with an ankle problem, Cook termed it a tough call.
“That’s the major decision we have to make,” Cook said on Saturday. “Yesterday when we turned up they had just watered the wicket so it didn’t give us too many clues.
“It will be really easy after the game in hindsight to see whether we’ve made the right decision but it will be a tough call.”
If England lose the series 2-0, they will slump to as low as sixth in Test rankings and Pakistan will jump to their best-ever second spot.
Cook, who hurt his groin during the second Test, said he was feeling better.
“I feel fine…. I’ve been confident since the second day after that game. The medical team worked pretty hard on me and I felt fine from there. Hopefully it will be as normal.”
England will also bring in James Taylor for Jos Butler to bolster their struggling batting.
“He’s itching to play and you don’t average 47-48 in first-class cricket without being a fine player,” said Cook of Taylor whose only two Test were in 2012.
“One of his very strong points is that when he gets in he goes on to get big scores. We know how important first-innings runs are to set the game up.”
Cook warned England will have to be at their best to beat Pakistan, unbeaten in a series in United Arab Emirates (UAE), being forced to play away from home due to security fears since 2009.
“They (Pakistan) have a good record in the UAE, at all three grounds. We’ve got to play some good cricket. If we continue to play the way we have, we’ve got to earn the right to do that here.”
Cook admitted Pakistan’s leg-spinner Yasir Shah will again be a major threat.
“He bowled very well. He’s got good control and bowls it pretty quickly for a leg-spinner. He’ll always take wickets because of the amount of overs he bowls in a four-man attack.
“Hopefully this game I won’t get out with him.”
Pakistan skipper Misbah-ul-Haq ruled out the option of playing a third spinner in Bilal Asif, whose bowling action was cleared on Friday.
“We have been thinking about it but the pitch doesn’t look like that sort of a turner where you can go with three spinners,” said Misbah.
Pakistan may bring in Azhar Ali to open the innings in place of Shan Masood and paceman Rahat Ali will replace fast bowler Imran Khan, ruled out with a hand injury.
Misbah said his team needed to remain focused.
“Obviously you have to think positively and we will do our best not leave any stone unturned and play well and win,” said Misbah, who deferred a decision to retire from Test cricket.
“Obviously your confidence is high after a win, so it’s an important match for us and we will do our best to win it.