Pears missed only two games after fracturing his leg against Carlton in round 18 before being brought back to face the Bulldogs.
He played the first half before receiving a heavy knock to the leg, forcing him to be subbed out of the game and miss Essendon's clash with West Coast at Patersons Stadium on Saturday.
"We probably made a little mistake by playing him," Hird said on Friday at Windy Hill.
"He had that small crack in his leg and got through half the game, and then got a significant whack on it.
"The doctors say if he rests it this week then it will be fully healed by next week so it was probably a bit of a mistake on my behalf to play him."
Promising 21-year-old Michael Hurley will also miss the important game against the Eagles with his troublesome 'stress reaction' injury in his foot.
Hird said if Hurley had the injury at the start of the season it would be handled differently.
"It's an injury that if he had at the start of the year you'd give him a full six weeks rest, but at the moment we think we can manage it with a couple of games, rest and [limiting] his training time," Hird said.
"It's a hot spot in his foot and there's a chance somewhere along the line that it might crack all the way through.
"We think if we played him this week it's an unnecessary risk for him."
Concerns over Dustin Fletcher's fitness have been allayed with the veteran defender flying to Perth a day before the majority of his team to prepare.
Despite Essendon needing only one more win to secure a finals berth, and the fact they play 17th-placed Port Adelaide next week at Etihad Stadium, Hird said he was taking a side confident of beating the Eagles.
"Our boys see it as a chance to go over and have a strong performance and hopefully a win against a quality team," Hird said.
"We've been able to run Collingwood and Carlton for a half this part of the season - earlier in the year we did a bit better than that - and we've beaten Geelong, and we beat West Coast earlier in the year.
"Our guys continue to get confidence from playing the best teams and, if you can beat them, you get some reward for your improvement."
Callum Twomey covers Essendon news for afl.com.au and essendonfc.com.au. Follow him on Twitter at @Cal_Twomey
