Midfielder Aaron Ramsey is set for another spell on the sidelines with a hamstring injury, while Arsenal could also again be without star winger Alexis Sánchez for their FA Cup fifth round tie with Middlesbrough on Sunday. Ramsey was forced off during Arsenal’s 2-1 win over Leicester City on Tuesday with what is his third hamstring problem of the season. Wenger, while confirming that the 24-year-old is set for two weeks on the sidelines, admitted that there was an underlying problem, but that the exact cause remains undiscovered.

“We haven’t found the underlying reason,” he said in his press conference on Friday. “There is an underlying reason that is certainly medical or bio-mechanical because he is a guy who is serious, works hard, has a controlled and disciplined life, so there’s no obvious reason why he should have muscular problems.

“We have individualized training for the players and prevention. I don’t think that is any special case that has been neglected, it’s just that we have to find a reason why that happens. It’s not a major injury, it’s a Grade One, it’s a small injury, a small muscular problem.”

Wenger also revealed that Sánchez “could be short as well for Sunday.” The club’s top scorer this season only returned from two weeks out with a minor hamstring problem in midweek, but suffered a knock to his knee against Leicester that eventually led to him being taken off. With Arsenal’s focus this season being on the upcoming resumption of the Champions League and their continued attempts to ensure they will be in the competition next season, it is unlikely that the former Barcelona forward will be risked.

The game may, though, be an opportunity to give Jack Wilshere some minutes on his return from injury. The English midfielder has been missing since the end of November after suffering the latest in a long line of ankle injuries. And while he returned to full training earlier this month, Wenger stressed that he badly needs some competitive action to regain his edge.

“He’s motivated and focused to come back as quickly as possible,” he said. “He worked very hard but he has still been out for [more than two] months and what he needs now is to get back. Competition gives you that sharpness that training cannot give you because it’s about a combination of fitness and decision-making - and speed of decision-making. It takes a while to get that back.”

After taking on Middlesbrough, the next two weeks see Arsenal face Crystal Palace with three crucial Premier League points on the line before hosting Monaco in the Champions League. They will have to negotiate all three fixtures, and quite possibly more, without the still injured trio of Alex Oxlade-Chamberlain, Mikel Arteta and Mathieu Debuchy. Arteta underwent ankle surgery a month ago and was expected to miss six weeks, while Debuchy was given a three-month prognosis to recover from a dislocated shoulder suffered on Jan. 11. And Oxlade-Chamberlain’s niggling groin problem continues to keep him sidelined.

“The closest of the three is Oxlade-Chamberlain. He might be two weeks away or three weeks away, maximum, the others are a bit longer.”

There is better news for this weekend, with Wenger stating that major January signing Gabriel Paulista is “very close” to making his debut. And given Wenger’s suggestion that he will rotate his lineup against Middlesbrough, Arsenal fans are likely to get a first glimpse of the former Villarreal center-back.