Liverpool have registered their interest in signing Newcastle United forward Alexander Isak this summer as they continue their search for a No. 9, a source has told ESPN. The Premier League champions are in the market for a new centre-forward as uncertainty over the future of Darwin Núñez continues, with Napoli one of the clubs interested in signing the Uruguay international this summer. Liverpool also turned down a €67.5 million (£78.5m) bid from Bayern Munich to sign forward Luis Díaz on Tuesday. The Reds have not submitted a formal offer for Isak however they have made an approach to Newcastle to assess his availability, as they have done with other forward targets. - Premier League 2025-26 kits: Ranking every jersey released - Why Liverpool have spent big to sign Florian Wirtz - Liverpool reject £58.6m Bayern Munich bid for Luis Díaz - source Newcastle's stance has so far been that they are unwilling to let the Sweden international -- who has scored 62 goals in 102 appearances for the club -- depart this summer. Liverpool have already broken their transfer record to sign Bayer Leverkusen playmaker Florian Wirtz in a deal that could rise up to a British-record £116m. It will likely take more than that for Newcastle to sanction Isak's exit this summer. Sources have also told ESPN Newcastle are working on a deal to sign Eintracht Frankfurt forward Hugo Ekitike, with a view to the forward playing alongside Isak in attack. Liverpool have also been liked with the player however it is understood they are not convinced by the 23-year-old, with Newcastle set to up their offer to Frankfurt in the coming days.