Southampton defender Florin Gardos is set to miss the next "six to seven months" with a knee injury.
His absence, together with Toby Alderweireld's departure to Spurs, leaves boss Ronald Koeman looking for a new centre-back.
Gardos, 26, made 11 appearances for the Saints last season, after signing from Steaua Bucharest, but was set to be given his chance this time round.
Koeman said: "That's the priority, to bring in one or two centre-backs."
Alderweireld's decision to join Tottenham, rather than convert his loan from Atletico Madrid into a permanent move, has heightened Koeman's need to strengthen his options at centre-back.
The Dutchman said. "It's too small with Maya [Yoshida] and Jose [Fonte].
"OK, we have [Jack] Stephens, we have [Jordan] Turnbull, but they are young and still they have to improve themselves."
The Saints have already signed Jordy Clasie, Juanmi, Cuco Martina, Cedric Soares and Maarten Stekelenburg this summer.
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