Pedro Mendes believes Kevin Thomson's return for Rangers will be like welcoming a new signing.
The Scottish Premier League champions have yet to add any fresh faces to their squad this summer, with the club's financial difficulties well documented.
A number of players have been shown the door, and further departures appear inevitable, but Walter Smith has not moved to bring in new recruits.
The Gers boss will, however, have highly-rated midfielder Thomson back in his plans this season, following eight months out with a cruciate ligament injury, and Mendes believes that news has come as a major boost to the Glasgow giants.
"I see Kevin Thomson coming back as a big signing for Rangers," he said.
"I think he will probably be the best signing this season. He is back for full training and getting back to fitness.
"He proved in the early stages of last season how good a player he is and how improved he is. He has improved his game in the last year or so.
"So, regarding new players coming in, Kevin Thomson will probably be the most important signing for Rangers this year."
Mendes also insists that the Gers' current crop of players, without any additions, is good enough to challenge domestically and in Europe next season.
"I think so. We have had a year of playing together and we know each other better," he added.
"Myself, I now know the club and exactly what is going on and about the SPL. We will be stronger this year.
"Regarding possible signings, that's up to the manager and the chairman. From a player's point of view, I think we have a very good team."
Meanwhile, American midfielder Maurice Edu has stepped up his rehabilitation from knee surgery and is now hoping to be back in action during the early stages of the 2009/10 campaign.
"I was on such a high after coming into the team and we had done well to win the league," he said.
"Even when I hurt my knee, I just thought it was a little injury and I had been looking forward to the cup final and winning the double.
"I'm glad we went on to get it but it would have been nice to have been part of that and missing out was a setback.
"The injury ruled me out of all the national team games over the summer (at the Confederations Cup) and that was a little bit disappointing too.
"I'm working hard to try to get over it and I'm focused on getting my fitness back and returning to the team again."