Arsène Wenger has admitted he would not have pursued the loan signing of Kim Kallstrom from Spartak Moscow had there been more time before the closure of the transfer window, with the veteran Sweden midfielder expected to be absent until mid-March with a micro-fracture of a vertebra.

Kallstrom, who has not started a game for the Russian club since 10 November, sustained the damage playing football on the beach during Spartak's warm-weather training break in Abu Dhabi two days before the cut-off. The 31-year-old's medical last Friday revealed the fracture but, with six hours before the deadline at that stage, Wenger deemed the loan worth pursuing to give himself an extra option for the campaign's daunting run-in, with the Swede his only addition during January.

The Arsenal manager, whose team returned to the top of the table by beating Crystal Palace 2-0, revealed that Spartak had agreed to pay Kallstrom's wages for the first six weeks while he recovers, with Wenger taking full responsibility for the deal despite the medical prognosis. "If you've played football, you might have played with a micro-fracture of a vertebra without knowing you had it," he said. "You don't even notice it. It crossed my mind [not to complete the deal] but I would not have signed him if we'd had two or three more days to do something.

"But it was 5pm on Friday night, so it was a case of sign him or nobody. We might need the players in March or April, you know, so it is a security and a free loan. We think four weeks is the best-case scenario; four to six weeks. The injury was an accident. Of course there's a possibility, like there is for every player, that he does not actually play for Arsenal but there is also the chance he scores a wining goal that's vitally important. We will only know if we're right or wrong at the end of the season.

"I made the decision because, across midfield, we have had players who have suffered injuries or suspensions: [Mathieu] Flamini, [Jack] Wilshere, [Mikel] Arteta, [Santi] Cazorla … they've all missed games and a part of the season. Even when they are back, a few of them might miss the next part, too. It's true that we have not sorted out the problem for the next four to six weeks but it was difficult to identify a player of Kallstrom's stature on a free loan and for the short term. You don't want to be locked into a deal for three or four years, where you pay them to do nothing. He has 108 caps for Sweden and played for seven or eight years in France, so I know the player well. I had a decision to make."

Alex Oxlade-Chamberlain, on his first Premier League start since the opening day of the season, scored the second-half goals to defeat Palace and send Arsenal back to the top with Manchester City to play Chelsea on Monday night. The England international, who scored his first club goals since December 2012 and his first of any kind since his country's 2-2 draw in Brazil last June, operated in central midfield alongside Arteta.

"I always believed he could play wide and central but that his future would be central," added Wenger, who will welcome Jack Wilshere back for Saturday's trip to Liverpool. "He's proved me right by scoring the goals but also in the quality of his performance. He was injured against Aston Villa on that 'famous day', and it took him a while to get back. But it's good to have him back."