Louis van Gaal said Ole Gunnar Solskjaer "parks the bus right in front of David de Gea" as he criticised the Manchester United manager again.
Solskjaer signed a permanent three-year deal last month after overseeing an upturn in results at United, however, the Red Devils have struggled since.
United – sixth in the Premier League and two points adrift of the top four – have lost two of their past seven matches in all competitions following a 4-0 Champions League quarter-final exit to Barcelona.
Former United boss Van Gaal, who initially questioned Solskjaer's approach after replacing Jose Mourinho in December, insisted the club favourite is defensive in his tactics.
"I can see how Ole had some impact in the beginning, because United were ninth in the table when he took over and the team was nothing," Van Gaal said via the Mirror. "United had been playing anti-football, as I call it, but don't think that Ole isn't afraid to park the bus either — he is more defensive than you think.
"I have been watching the team, because I always look at United still, and Ole parked the bus against Arsenal. He did it against Tottenham in the league. And at stages against Paris Saint-Germain and Barcelona in the Champions League.
"He plays against all the big teams like that. The emphasis is more on defending than on attacking or wanting to play dominant football. I actually call it parking the bus. Ole does it not just outside the 18-yard box. He parks the bus right in front of [goalkeeper] David de Gea."
Van Gaal – who was sacked by United after winning the FA Cup in 2016 – added: "When United play that way, they play 4-4-2 and play counter attacking football with Marcus Rashford and Romelu Lukaku. They are gambling on the speed of those two because they are faster than their opponents when they get the space. Rashford’s pace is incredible. You don’t catch him when he breaks away.
"But if Man United want to be a dominant force in Europe again - and in England - they have to have a different playing style.
"The problem as a foreign manager is that you find out that the English football culture is different from Germany and Spain. In those countries, you work on things in training. In England, everything is done by playing matches. They get fitter or gain stamina by playing lots of matches. It is a culture you cannot change easily. I wanted to change things, but it proved very difficult."