Dominic Thiem admitted he needs more time to be able to complete after his frustrating return from injury continued with a "painful" French Open first-round exit to Hugo Dellien.

Thiem also hinted he could drop down to play a couple of ATP Challenger-level tournaments, having struggled upon his return from a wrist injury which ruled him out for the second half of last season.

The 2020 US Open winner, who was runner-up to Rafael Nadal at Roland Garros in both 2018 and 2019, arrived in the French capital on a six-match losing run, and Dellien took full advantage of the Austrian's woes to claim a 6-3 6-2 6-4 win.

Speaking after a comprehensive defeat in which he was broken four times, Thiem acknowledged he is not operating at the necessary level to compete at grand slams.

"It was not a good match at all, but it is what it is," a dejected Thiem said post-match.

"You've got to take time, as the level is extremely high from all the players competing here, and I'm not there yet. I was really working hard to get there, but the time was just not enough, I've got to accept it.

"Even though there have been some really painful defeats now week after week, still nothing unexpected happened. Had I won a lot of matches, it would have been a big surprise, so it's painful.

"I'm very disappointed, but the wait goes on."

Since his comeback, the former world number three has only won one set of tennis in seven matches - at an ATP Challenger Tour event in Marbella in March - and he thinks a return to that level could aid his recovery.

"The problem is a match situation is something different; [in a] grand slam especially," he added. "I am definitely thinking to go back to Challenger level for one or two tournaments.

"I am more tight, more nervous, and the whole body gets more tight. This is toxic to my forehand because I am still missing the fine feeling there."

Dominic Thiem's miserable return from injury took another turn for the worse when he was dumped out of the French Open by the unheralded Hugo Dellien on day one.

Thiem, who missed the second half of last season due to a wrist injury, arrived at Roland Garros on a six-match losing streak.

The Austrian was totally out of sorts once again on Court Simonne-Mathieu and Colombian Dellien capitalised, winning 6-3 6-2 6-4 on Sunday.

A two-time runner-up at the clay-court grand slam in Paris, Thiem has only won one set in seven matches since making his comeback - and that was at an ATP Challenger Tour event in Marbella in March.

The 2020 US Open champion racked up 42 unforced errors and did not have a solitary break point on another difficult day.

The 28-year-old had a first-serve success rate of only 59 per cent as world number 87 Dellien moved through to round two at Roland Garros for only the second time.

Thiem struck 29 winners to Dellien's 15, but the former world number three was broken four times as he crashed out.