Emir Spahic has completed his move from Sevilla to Bayer Leverkusen for an undisclosed fee.
The 32-year-old defender spent two years with the Spanish outfit, but saw out the latter part of last season on loan at Russian club Anzhi Makhachkala.
It was the Bosnian international's third spell in Russia, having previously played for Torpedo Moscow and Lokomotiv Moscow.
Bayer, third in last season's Bundesliga, have moved swiftly to add Spahic to their ranks.
Premier League new boys Palace agreed an undisclosed fee for Gayle on Thursday and they were given permission to hold talks with the player.
Terms are thought to have been agreed and Gayle is now having a medical as he closes in on a move to Selhurst Park, Sky Sports understands.
Gayle impressed at Peterborough last season after arriving initially on loan from Dagenham & Redbridge before making the move permanent in January.
The 22-year-old scored 13 goals in 29 games for Peterborough, but they were always facing a battle to keep him following their relegation to League One.
A number of clubs, including Fulham, have been linked with Gayle, but it appears Palace are on the verge of landing the former Arsenal youngster.
Palace are also close to signing former West Brom winger Jerome Thomas with the free agent also undergoing a medical at Selhurst Park as Ian Holloway looks to make the pair his first signings of the summer as he prepares for life in the Premier League.
McDermott joins on a one-year contract after being released by Newcastle where he came through the youth system.
The 21-year-old is the son of former Liverpool and England midfielder Terry McDermott, who himself had a spell at Gigg Lane at the start of his career.
Cameron had been offered a contract by Northampton, for whom he played six games on loan at the end of last season but the offer was withdrawn by the Cobblers after he stalled on signing.
The defender, also 21, rose through the ranks at Coventry and played 52 times for the Sky Blues before being released at the end of last season. He signs a two-year deal.
The duo join Gareth Roberts, Euan Holden and Ashley Grimes, who all joined the League Two club on Thursday.
