Messi departed the club last summer after more than two decades in Catalonia, joining Paris Saint-Germain on a free transfer after financial difficulties left him unable to sign a new deal with Barcelona.
The 35-year-old signed a two-year deal in the French capital which runs until June 2023, when he could again become a free agent.
Speculation has therefore grown that Messi might consider returning to Barcelona, now under the management of long-time teammate Xavi.
While the club continues to face financial challenges, Romeu believes that the board can “make miracles happen” to bring the seven-time Ballon d’Or winner back.
“If the club want [to bring him back], we will get to work [in working out a deal],” Romeu said.
“We know how to make miracles happen. The doors are always open for Messi.”
The former Barcelona captain scored nearly 700 times for the club after making his senior debut in 2004.
Messi has recaptured some of his best form at the start of the new campaign, helping PSG to an unbeaten start in Ligue 1 and the Champions League.
A World Cup crown is the one attainable major trophy that eludes the great Argentine, who conceded this week that the tournament in Qatar this winter is likely to be his last.
“It’s my last World Cup, surely,” Messi told ESPN.
“I’m counting down the days to the World Cup. There is anxiety and nerves at the same time. Wanting it to be now, what is going to happen, and ultimately, how is it going to go?
“In a World Cup, anything can happen. All the matches are very tough. The favourites don’t always end up winning.
“I don’t know if we’re the favourites, but Argentina is always a candidate because of its history. Now even more so because of the moment we’re in, but we are not the favourites. I think there are other teams that are above us.”