Sub-zero conditions threaten Europa ties
Two round of 32 second-leg matches are scheduled to be played in Russia on Thursday with temperatures expected to be hovering around minus 15 Celsius, considered the safe minimum under FIFA and UEFA guidelines.
Last week, Dutch champions Twente Enschede played under protest away to Rubin Kazan amid confusion over the real temperature.
Tijs Tummers, secretary of the technical committee at the international players' union FIFPro, told Reuters there had been discrepancies in readings.
"On all thermometers the temperature was minus 16 or minus 17, only the thermometer of UEFA gave a temperature of 14.9 Celsius," he said.
"FC Twente and UEFA have agreed to evaluate the procedure of last week to prevent problems like this happening in the future."
Tummers added that media reports had said the temperature dropped as low as minus 23 Celsius, even though the game had been brought forward to lunchtime from the originally-planned kick-off at 9pm local time.
The combination of early kick-off, freezing weather and new venue - it was even colder in Kazan itself - resulted in the match being played in front of 500 people in a 90,000 seater stadium.
Twente won 2-0 and can look forward to playing the return in relatively balmy temperatures just above freezing but the visitors to Russia face extremly challenging conditions.
Greek side PAOK Salonika battled to a 1-1 draw at CSKA Moscow on Tuesday but the Russians progressed to the last 16 2-1 on aggregate.
Spartak Moscow entertain Swiss champions FC Basel on Thursday with a 3-2 lead from the first leg and Zenit St Petersburg, Russian champions and 2008 UEFA Cup winners, face Young Boys trailing 2-1.
Five-times European champions and three-times UEFA Cup winners Liverpool are arguably the biggest club still in the competition following the group-stage exit of Juventus.
Kenny Dalgish's team barely mustered a shot on goal last week in Prague against a side who, like many of the eastern European teams, had been inactive for the previous two months due to the winter break.
Former European champions Ajax Amsterdam should cruise through, having won 3-0 at Anderlecht in the first leg, as should Germany's Bayer Leverkusen, who have a 4-0 lead at home to Metalist Kharkiv.
Big-spending Manchester City take a 0-0 scoreline into their home leg following last week's stalemate away to Greeks Aris Salonika.
Portuguese pair Porto and Benfica, both former European champions, have 2-1 leads from the first legs as Porto host Sevilla on Wednesday and Benfica visit VfB Stuttgart on Thursday.
The leaders of the Dutch and French leagues, PSV Eindhoven and Lille, meet again on Thursday, having produced a storming 2-2 draw in last week's first leg.
Napoli, Italy's sole survivors, appear to be the outsiders against Villarreal after being held 0-0 at home by the Spaniards.