The 24-year-old has been a shining light in what has been a disappointing return to the Premier League for Dean Smith's men, scoring seven goals in 31 outings.
However, he was powerless to prevent Villa succumb to a 2-0 defeat to Premier League champions Liverpool at Anfield on Sunday.
Former Reds midfielder Souness believes Grealish has to be better on the ball if he is to be considered one of the league's best.
"I would not want to have been the most fouled player in the Premier League. That means I'm holding onto the ball too long, I'm taking extra touches when I don't need to," he told Sky Sports.
"It means you're not seeing the picture quickly enough. There's no doubt about it. He's easy on the eye, he's silky on the eye, but I'm yet to be convinced by him."
Emile Heskey disagreed with Souness, arguing that Grealish takes so many touches because of a lack of quality good movement around him.
"When I was being coached at Liverpool, I was told, I make the striker's mind up, with my body movement, with the way I get the ball out of my feet, with my body movement. I make them run where I'm looking like I'm going to kick the ball," Souness added.
LATEST FOOTBALL NEWS
worth the wait
Adams nets screamer as Southampton down Man City at St Mary's
news
Man United news live: Rashford optimistic about Greenwood - do they need Sancho?
CHAMPIONS
Keita provides inch-perfect assist for Mane goal as Liverpool earn win over Villa
super
Top ten scoring defenders ever, including Man Utd, Real Madrid and Barcelona legends
gem
'Total one-off' Vardy hailed by former non-league owner after striker joins PL 100 club
PL BOUND?
Man City could sign Messi next year if Guardiola leaves the club, talkSPORT told
Backed
Man United shouldn't spend big on Sancho - they have Greenwood, talkSPORT told
tricks of trade
Chelsea boss Lampard learnt 'ruthlessness' from Mourinho, talkSPORT told
CRIS OF LIFE
Ronaldo ends two shock Juventus streaks with free-kick against rivals Torino
Frustration
West Ham remain in relegation trouble as they surrender lead twice at Newcastle
"I just think that anyone who gets that many fouls, is not seeing the picture quickly enough.
"As an old midfield player, I always think: 'Would I like to have played against him?' I'd have loved to have played against him because he allows me to get to him, to get physical with him.
"Do I want to play against Paul Scholes, Xavi, Andres Iniesta, who pop it off one or two touch? I want to play against people like him because I know he's going to let me mess him around."
Graeme Souness has claimed he would have 'loved' to have played against Jack Grealish in a scathing criticism of the Aston Villa captain.
Almere City FC 
Ajax 
Spartak Moscow 
Orenburg 
Lyon 
Stade Brestois 29 
Barcelona 
Real Sociedad 
Montpellier 
Rennes 
Bari 
Sampdoria 
Manchester Utd 
Fulham 
Roma 
Como 
Marseille 
Nantes 
AC Milan 
Lazio 
Osasuna 
Valencia 
Juventus 
Verona 
Villarreal 
Espanyol 
Borussia Dortmund 
Lille 
PSV 
Arsenal 
Real Madrid 
Atletico Madrid 
Feyenoord 
Inter 
Bayern Munich 
Bayer Leverkusen 
Benfica 
Paris Saint Germain 
Liverpool 
Montevideo City Torque 
Union Espanola 
Everton 
Dynamo Kyiv 
Shakhtar Donetsk 
Kryvbas Kryvyi Rih 
AZ Alkmaar 
Tottenham 
FCSB 
Fenerbahce 
Rangers FC Andorra 
FC Copenhagen 
Chelsea 
Panathinaikos 
Fiorentina