David Luiz has extended his stay at Arsenal until the end of the 2020-21 season after the club triggered the option of a second year in his contract, putting an end to speculation that his spell would conclude this month. The Guardian understands the centre-back, who is among the club’s highest earners and had been considered vulnerable to their precarious financial situation, has accepted the offer to continue with Mikel Arteta’s side. Barring any unforeseen late hitches before Tuesday’s midnight deadline he will stay on the books until next June, when he will be 34. Arsenal are also expected to confirm that the loanees Dani Ceballos, Cédric Soares and Pablo Marí will stay at the club until at least the end of the 2019-20 season, with the latter two on course for permanent deals from Southampton and Flamengo respectively. Doubts over David Luiz’s future had increased further after he was sent off to end a disastrous substitute cameo in the 3-0 defeat at Manchester City last week but Arteta had remained keen to secure his future. With Marí now set to miss two or three months after injuring an ankle at the Etihad Stadium, Arsenal’s defensive options would have been limited had no deal been agreed. It is the latest development in a mixed 24 hours for Arteta, who endured another injury setback on Tuesday with the news that Gabriel Martinelli has sustained a serious knee injury towards the end of Monday’s training session. The forward is likely to be out for a number of months, but the goalkeeper Bernd Leno will not be sidelined for as long as the club had feared. Martinelli has had an outstanding first season in England, scoring 10 goals after joining from the Brazilian lower-league club Ituano. But the 19-year-old seems sure to miss the start of next season, with Arteta admitting the prognosis is bleak. “In training he got hit by another player and damaged his knee,” Arteta said on Tuesdayyesterday. “The doctor is assessing the extent of the injury, but it’s not looking good at all. We don’t know, but it’s looking like months.” Arsenal had feared similar news on Leno after he hyperextended his knee following a late challenge from the Brighton forward Neal Maupay in the 2-1 defeat on Saturday. The German’s injury is less serious than expected and he should return to training within four to six weeks. Realistically that rules him out of the rest of this campaign, meaning Emiliano Martínez will deputise, but it saves Arteta a potential transfer market headache at a time when finances look painfully tight. Those constraints should not prevent a deal for Marí, who joined on loan in January. “We’ve been trying to get the deal done because we were happy with what Pablo can bring to us and the club were trying to finalise the deal,” Arteta said. On the subject of Soares, the loanee right-back from Southampton who is yet to make an appearance due to injuries of his own, he struck a similar note. “It was the plan from the start. He hasn’t played at all for us, but again, we think he’s a player that will improve and will help the squad depth.”