The Premier League's top two have both invested in young talent as they strengthen ahead of the run-in.
Arsenal confirmed the signing of defender Jakub Kiwior from Italian side Spezia. Also on Monday Manchester City announced they had signed Argentine midfielder Maximo Perrone from Velez Sarsfield.
The 22-year-old Kiwior featured for Poland at the World Cup in Qatar and was in the stands at Emirates Stadium on Sunday evening to watch his new side beat Manchester United.
Kiwior, who had a spell in Belgium with Anderlecht earlier in his career, moved to Serie A from MSK Zilina in August 2021, and made 43 appearances during his time with Spezia.
Arsenal said Kiwior, a left-sided central defender, had signed a long-term contract, with the fee reported to be in the region of $A37m.
"He's a young versatile defender who has shown huge potential and qualities with Spezia in Serie A and also at international level with Poland," Gunners boss Mikel Arteta told the club's website.
"Jakub is a player who will add strength and quality to our defensive unit. We welcome Jakub and his family to Arsenal and look forward to working with him."
Perrone has been signed on a contract until 2028, City said.
The 20-year-old scored three times and provided two assists after making his debut with the Buenos Aires-based team in March.
Perrone is currently playing in the Under-20 South American championship and at City will join compatriot and World Cup winner Julian Alvarez, who arrived in Manchester last year.
Aston Villa signed teenage striker Jhon Duran from Chicago Fire in an $A32m deal.
Duran, 19, has scored eight goals in 28 appearances for the MLS club.
Villa will pay $A26m for Duran, who has three caps for Colombia, and a potential $A6m in add-ons.