Crystal Palace have signed Naouirou Ahamada from Stuttgart for 11m euros (£9.7m), while Arsenal's Albert Sambi Lokonga has joined the club on loan.
The midfielder has scored twice and contributed two assists in 17 starts for the Bundesliga side this season.
Meanwhile, Lokonga, 23, will join the Eagles until the end of the season.
The Belgian holding midfielder has made 15 appearances in all competitions for Premier League leaders Arsenal this campaign.
Ahamada represented France at under-18 level and spent time in Juventus' academy before joining Stuttgart in 2021.
"I'm very happy to have joined this club.