Jack Wilshire has suffered a setback in his return from injury, Arsene Wenger confirmed Friday.
The 20-year-old England midfielder has not featured this season after he picked up an ankle injury during a pre-season game against New York Red Bulls in July.
The Arsenal star was expected to return at the end of this month after he underwent surgery in September.
Indeed, Wilshire returned to training earlier in January and appeared optimistic about making Arsenal's Champions League last-16 first-leg tie away to Milan on 15 February.
However, Wenger revealed that the dynamic midfielder had suffered a fresh injury scare and the club will now await the results of a scan before making a decision over his return.
"Wilshere had a little setback which is under investigation," the Arsenal manager told Sky Sports.
"We don't know yet how bad it is. He has pain again in his ankle [when running]. We stopped him right away. He is seeing a specialist today, so I do not want to give you any wrong information."
Meanwhile, Arsenal forward Theo Walcott has praised the contribution of Bacary Sagna after the French defender returned to full training this week.
Sagna has been side-lined since breaking his leg against Tottenham back in October but is in contention to feature against Aston Villa in the club's FA Cup fourth round tie on Sunday.
"Bac shows good qualities at right back," he told Arsenal.com. "We have had players come in and do fairly well considering they are not full backs but Bac is a player I bond very well with on the pitch.
"We work very well together and get on great. It's nice to see him back, because that memory of Tottenham when he broke his leg is not nice.
"It's good to see him smiling again and enjoying training. He is a player that I think we have missed."