Former Aston Villa striker Stan Collymore feels Martin O'Neill was sold short by owner Randy Lerner during his time in charge of the club.
O'Neill resigned as manager of Villa late yesterday.
"He's eminently frustrated with a lack of movement in the transfer market and a lack of backing to go out and buy players," Collymore told talkSPORT.
"People say he's spent a lot of money over the last couple of seasons but you have to keep spending if you're going to be competitive.
"The club was on its backside [when he took charge]. He dragged them up from near the bottom of the table into a position where they were challenging at the top and he's brought in a lot of good, young English players.
"Villa's in a good place as a club and he deserved more backing. It's got a little frustrating for him and, as with all good quality managers, if they're not getting the backing they think they deserve, they'll turn their back on the club.
"Aston Villa needs to kick on. Man City are spending, Liverpool are spending. It's not good enough for a club like Villa to be happy with sixth, seventh or eighth.
"Martin O'Neill wanted to take them on to the next level and he deserved the backing to try to do that.
"He deserved top-dollar investment on an annual basis and I, as a Villa fan, don't feel he got that."
