Haskell, who appeared to go in high, sparked the anger of the home fans but escaped a card from referee JP Doyle who, after consulting television match official David Grashoff, deemed the tackle worthy of only a penalty in the way of punishment.
"It wasn't the greatest hit of all time," said director of rugby McCall. "Alistair's on his feet but he's a bit groggy. I think a penalty on its own could be regarded as a bit lenient."
Wasps rugby director Dai Young saw it differently, stating: "I thought it was a good tackle.
"First and foremost, we hope the player's okay because nobody likes to see anybody going off, but the tackle looked okay to me."
The incident concluded an eventful day for Hargreaves, who had earlier scored Sarries' only try and been sin-binned for going over the top at a ruck.
Charlie Hodgson kicked seven penalties from seven attempts, though he missed the conversion after Hargreaves' charge-down score, and Nils Mordt also slotted a three-pointer while on as a blood replacement for Hodgson.
Tom Varndell and Charlie Davies scored tries for Wasps, who crucially missed three penalties and a conversion.