According to Fabrizio Romano, the two parties have reached a verbal agreement, with an announcement expected within the next 48 hours. Mingueza has been a free agent since June, when his contract at Celta Vigo expired.
The 27-year-old joined Celta from Barcelona in the summer of 2022 and went on to make 147 appearances for the Galician club, having previously featured 66 times for Barcelona's first team after coming through the club's academy.
Versatile enough to play at right-back or in central defence, Mingueza gives Sage a low-risk option to strengthen a defence that has already lost Marc Guehi this year, with Chelsea's interest in Maxence Lacroix adding further uncertainty to the position.
Crystal Palace won the Conference League under previous manager Oliver Glasner last season, who has since departed to take charge at Nottingham Forest, prompting the move for Sage after his impressive spell at Lens.
The Mingueza deal is expected to be the first of several additions at Selhurst Park this summer as Palace prepare for a campaign that will include European football alongside their Premier League commitments.
Palace had reportedly identified Mingueza as a "secret" priority target, with Arsenal and Newcastle also credited with an interest in the defender earlier in the window. Getting the deal wrapped up quietly and without a prolonged saga will be viewed internally as a promising early sign for Sage's tenure, particularly given the club's summer had otherwise been relatively quiet in the transfer market up to this point.
The versatility Mingueza offers is expected to prove valuable over a long campaign that will stretch Palace's squad further than in previous seasons, with injuries, suspensions and fixture congestion all factors as the club juggles domestic and continental commitments.
Sage is still expected to look at further reinforcements, particularly in attack, as he continues shaping his first squad since arriving from Ligue 1.