Manchester City signed Nico Gonzalez from Porto in the biggest move from Premier League clubs on Monday's transfer deadline day, while Bayern Munich's Mathys Tel headed to Tottenham on loan.
City's midfield frailties without Ballon d'Or winner Rodri, who is out for the season due to a serious knee injury, were exposed in a 5-1 thrashing at Arsenal on Sunday.
Pep Guardiola's men find themselves in a battle just to qualify for next season's Champions League, with the defending champions sitting fifth in the Premier League, 15 points behind leaders Liverpool.
City were also in need of reinforcements for a blockbuster Champions League play-off round tie against holders Real Madrid later this month.
Former Barcelona midfielder Gonzalez, 23, arrives for a reported fee of 60 million euros (GBP50 million, $62 million).
"This is the perfect opportunity for me at this stage of my career," said Gonzalez.
"I know the reputation Pep has and I cannot wait to work with him. In fact, I am honoured he wants me to play in his team."
City have already splashed out more than GBP120 million in January on Egypt forward Omar Marmoush and young defenders Vitor Reis and Abdukodir Khusanov.
Tottenham were busy in the final hours of the window as they bolstered Ange Postecoglou's injury-ravaged squad.
Tel reportedly turned down the opportunity to join Spurs earlier in the window after a GBP50 million deal was agreed with the German giants.
But the French under-21 international has now moved to north London until the end of the season with an option to make the move permanent in the summer.
Spurs, though, were frustrated in their bid to add more defensive recruits on deadline day.
The BBC reported Crystal Palace rejected a GBP70 million bid for captain Marc Guehi, who has just 18 months left to run of his contract at Selhurst Park.
Chelsea's Axel Disasi had been linked with a move across London, but is instead set to join Aston Villa, who also added more firepower with the signing of Marco Asensio on loan from Paris Saint-Germain.
The Spaniard, who won three Champions League titles with Real Madrid, joins Marcus Rashford as new options for Unai Emery's forward line after the departure of Jhon Duran to Saudi side Al Nassr.
However, there were no deadline day deals for Premier League title contenders Liverpool and Arsenal or struggling Manchester United.
Arsenal's bid to strengthen their forward line appears to have been frustrated after Villa rebuffed an offer for England international Ollie Watkins last week.
United boss Ruben Amorim said the club were "trying everything to improve the team without doing mistakes of the past" following Sunday's 2-0 defeat to Crystal Palace.
The Red Devils are wary of breaching profit and sustainability rules and were reportedly put off a move for Tel due to Bayern's demand for a loan fee.
West Ham completed the loan signing of Brighton striker Evan Ferguson, who is reunited with his former manager Graham Potter.
The Seagulls replaced Ferguson with highly-rated Greek forward Stefanos Tzimas, who had been linked with Liverpool, but will remain at Bundesliga 2 side FC Nuremberg for the remainder of the season.
Former England left-back Ben Chilwell joined Crystal Palace on loan from Chelsea until the end of the season.
