The La Liga expert has claims Manchester United pulled out because they couldn't compete financially with City.
The highly rated Argentine defender is expected to complete a big money move to the Etihad this week after seemingly forcing his way out of current club Valencia.
He is likely to be the long-term partner for Vincent Kompany at the heart of Manuel Pellegrini’s defence, with Eliaquim Mangala having failed to impress in his first season at the club.
And Armstrong has backed Otamendi to be a big hit at City, while saying he will be a better partner than Mangala has proved to be.
“I believe he [Otamendi] will go on to become a big hit at City,” he wrote on Kicca.
“He is the perfect fit for the Premier League and even though he is relatively short for a defender he reads the game well and is very mobile. He will be a better partner for Vincent Kompany than Mangala has been.”
Claims Manchester United could not compete financially
The Argentine defender has been hot property this summer, with a number of big clubs, including Real Madrid and Manchester United, both being linked with a move for him.
That speculation only increased once it became evident that the player was keen on a move away from the Mestalla, despite only being at the club for a relatively short time.
It seems City have won the battle for his signature though, and Armstrong says fierce rivals Manchester United pulled out as they knew they couldn’t compete with City’s vast finances.
“Otamendi is also very ambitious and he made it clear to the club he wanted to move to the Premier League,” he added.
“I hear United pulled out of the hunt for him as soon as they heard City were involved because they knew they couldn't compete when it comes to paying the wages Otamendi will demand.”