Sometimes it is hard to realize that Gael Monfils has been back in tennis for all of 2013. Granted, he has never really been a threat at majors because he struggles to play his best tennis for more than a few matches at a time on the biggest stages. But he can definitely threaten the top players and is a scary draw for anyone. At least, he was until last year.

Monfils is probably best known for his showmanship on court, but he is almost as famous for his sometimes ridiculous slides to attempt to get to balls. And, as Monfils learned last year, sliding like that on hard courts is not good for the knees. Monfils missed almost all of the last seven months of the 2012 season with a knee injury, and there were serious concerns that it could affect the rest of his career.

The flamboyant Frenchman made his real comeback (after a failed attempt in September) early this year and has had fairly respectable results since then. He reached the semifinals in Auckland and followed it up with a solid showing in Melbourne. He upset Alexandr Dolgopolov along the way, but he could not edge past fellow Frenchman Gilles Simon in the third round.

Monfils has not reached the quarterfinals of any tournament larger than an ATP 250 this year, which explains why he has flown so much under the radar so far. He did reach the final in Nice but could only follow it up with a third-round showing at Roland Garros. Still, Monfils did upset No. 6 seed Tomas Berdych there, so his performance surpassed expectations. But, having defeated Berdych, losing in the third round to Tommy Robredo felt disappointing. He was forced to skip Wimbledon but has had a respectable summer overall, even if not quite up to his usual standards.

Monfils seems to have peaked in the weeks before majors this year, with the aforementioned good runs at Auckland and Nice as well as an appearance in the Winston-Salem final last week. He seems to be recovering some semblance of his old form, playing very well in Winston-Salem and putting up a tremendous performance to blast Adrian Ungur off the court in the first round at the US Open. Ungur played poorly, to be sure, but that should not take away from how strong Monfils looked.

If there is a problem for Monfils, it could be that he is not perfectly healthy once again. He retired from the Winston-Salem final against Melzer with an apparent hip injury, but he was already down a set at that time, and perhaps he just needed some more rest before the US Open. He looked fine out there today, but an average first-serve speed of only 101 miles per hour raises some concern.

Even if he is healthy, though, Monfils will have a tough second-round match against John Isner on Thursday. The American played one of the best matches of his career today and looks like he can finally play well with other pros from the baseline. If Monfils’ serve is at its usual level, though, Isner will struggle to earn break points no matter how well he plays. Monfils is capable of incredible gets and might make some chances for himself against the Isner serve if he’s healthy. This seems like a match built to reach tiebreaks.

Monfils’ health feels like the big question every time that people talk about him now. If it is no longer an issue, he needs his game to follow. He was a dangerous sleeper in majors before the injuries came. Monfils will need to make a statement against Isner if he wants to become one again.