Nottingham Forest have landed Austria international Xaver Schlager on a free transfer.
The 28-year-old will sign a two-year contract, with the option of a further 12 months, after opting against extending his stay at RB Leipzig, according to reports.
Schlager was previously a "target" for Celtic. The move raises questions about Forest's continued interest in midfielder Arne Engels.
The club had several bids for the 22-year-old rejected in January, including one believed to be worth £25 million, which would have equalled a Scottish record sale.
Forest are not the only club interested in Engels, as Crystal Palace, Fulham, Lazio, and Roma are all keeping an eye on the player's situation.
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The move does not necessarily mark the end of Forest's pursuit of Engels, with the club looking to reshape their squad under new manager Oliver Glasner.
Celtic manager Martin O’Neill acknowledged the interest in Engels, saying: "I would imagine so, yeah. At this minute, I don’t think anything has happened.
"Where it carries on up towards the end of the window, then suddenly something happens, you’re not ready because it’s happening too late.
"All those bids Nottingham Forest made came in at the 11th hour, so that was just a non-goer for us at that particular stage.
"Then he got injured just after that. So if some things can happen a bit earlier, then maybe there’s some resignation on my part there too."