The scrutiny may be especially intense in the case of Stan Collymore, who scored twice against Liverpool in Gregory's first match as manager, but has not played since suffering a groin injury during Villa's 1-0 defeat by Atletico in the first leg of their Uefa Cup quarter-final.
Collymore declared himself fit yesterday, while Julian Joachim shrugged off a knee injury sustained during Saturday's win over Crystal Palace. Both are vying for a place alongside Dwight Yorke, whose inclusion is assured, and possibly Savo Milosevic, who scored twice against Palace without particularly impressing Gregory.
The likelihood is that Villa will turn to Collymore, perhaps keeping Milosevic in reserve, with Joachim a candidate for a role wide on the right of midfield. But Gregory may well have had the pounds 7m striker in mind when he said he wanted to be sure that certain individuals were prepared for a potentially explosive contest.
"I shall make eye contact with them at training because you can always read things from doing that," he said. "I'm one for studying carefully every little thing they do, to see whether they are ready for it and whether they've got fear or excitement in their eyes."
A fired-up Collymore can be an awesome prospect for defenders, as Liverpool discovered. That success was one of three in Gregory's first four Premiership games as Brian Little's successor, but he knows it will take an exceptional performance to win by two goals.
"I don't expect us to go for the jugular from the first minute.There has to be a certain amount of caution, though I don't envisage us sitting back and trying to nick one.''
Atletico are unbeaten in seven European away matches under Raddy Antic, who is an arch exponent of counter-attacking football. Nevertheless, they arrived in Birmingham under a cloud. Their president, Jesus Gil, questioned whether it was worth turning up tonight after Saturday's 2-1 defeat by Campostella. "I am disgusted with them. A lot of the players don't care about wearing the Atletico shirt," Gil said. "We need to go out with the attitude of Aston Villa and fight for the world."
The man charged with keeping emotions under control is Mario van der Ende, the Dutchman who refereed so expertly when England met Italy in Rome last October.
Ten home players and seven from Atletico start the evening knowing a yellow card would put them out of the semi-final first leg, although Villa have received unexpected encouragement in one instance.
Mark Bosnich was cautioned for time-wasting when he sought to draw attention to his bombardment by the crowd in Madrid. Despite the absence of a formal appeals procedure, the Villa secretary, Steve Stride, wrote to Uefa, pointing out the "strange circumstances''. The ruling body's disciplinary committee have promised to examine the case on 23 March.Reuse content