The Jambos host the Hoops at Tynecastle on Sunday in the fourth round of the Scottish Cup.
Neil Lennon's side had gone almost two years without conceding from a corner, only to do so twice during their 3-0 defeat to the Italian giants as their Champions League hopes ended.
But Locke anticipates the Celtic manager will have drummed into his players that they cannot afford any more lapses such as the ones that ensured they will finish bottom of Group H.
Locke said: "Celtic pride themselves on defending set-plays. I'm sure Neil never saw the goals they conceded coming because they have been really good defensively since the start of the season and have not lost a league game.
"That will be something he will be working on over the next few days and I don't think we will get it so easy."
Meanwhile, Locke believes Friday's crucial creditor's meeting at Tynecastle is more important than the cup clash with holders Celtic.
The Edinburgh club entered administration in June with debts of about £30million, which brought with it a 15-point deduction for the start of the season and a signing embargo.
Fans group the Foundation of Hearts have put forward a financial package worth £2.5million which will be submitted to creditors on Friday, seven days before it goes to shareholders.
But in each meeting the fate of the Company Voluntary Arrangement (CVA) lies in the hands of Lithuanina-based Ukio Bankas and UBIG, which are owed the vast majority of money and together own about 80 per cent of the club's shares.
The creditors' meeting was supposed to take place last week but was delayed by administrators BDO.
Now Locke hopes the future of the club can be decided upon once and for all.
He said: "It's a massive week for us. I just hope everything goes to plan for us tomorrow, while we've got a huge game on Sunday as well.
"But as far as the long-term future of the club is concerned, tomorrow's meeting is much more important.
"We have done everything we possibly can to find a solution and the staff, the players and the fans are all desperate to see the club moving forward again. The only way we will do that is by a CVA."