Ramsey was injured after coming off the bench during Tuesday’s FA Cup win at Hull, and newspaper reports this week suggested his participation at Euro 2016 might even be under threat.
But Wenger has put those concerns to bed, even if the severity of the problem has taken him by surprise.
Speaking ahead of Sunday’s quarter-final against Watford the Arsenal boss said: “No, he’s not out for the season. I don’t think that.
“His clinical signs are quite positive, and I would say four weeks. It’s a bit worse than what i thought because usually when a player gets injured he stops – I had the feeling it was just a precaution and he would be fit for Sunday.”
Mertesacker took a blow to the forehead but has trained since, while Gabriel (hamstring) is expected to rejoin the group on Saturday, when Laurent Koscielny could also be back.
“I will take advice from the medical people, and after that if he is available I will do it,” Wenger said.
Watford’s training ground is adjacent to Arsenal’s, and Wenger joked he had sent up a drone to monitor Quique Sanchez Flores’ preparations for Sunday.
Strikers Odion Ighalo and Troy Deeney have been identified as the main threat, and
Wenger said: “They’ve done extremely well – it looks like the Championship teams who come up deal very well now with the Premier League regime.
“They are well prepared, and the two strikers are very efficient. We have to work very hard to control the game.”