May 24 (GMM) The engine deal between Toro Rosso and Renault is reportedly not yet ready to be announced.

Earlier this week, we reported that the Red Bull-owned team's anticipated switch from Ferrari power would be announced imminently, on the sidelines of the Monaco Grand Prix weekend.

Jean-Eric Vergne, Scuderia Toro Rosso STR8
Jean-Eric Vergne, Scuderia Toro Rosso STR8

Photo by: XPB Images

But German-language Speed Week reports that, during conference calls and internal meetings in the last days, there were still elements of the deal that were being discussed and debated.

"There are still too many outstanding issues," a Toro Rosso source is quoted as saying.

Alain Prost, on Renault's executive committee, said on Thursday that he expected progress to be made this weekend as the French marque signs up its 2014 customers.

"I'm not negotiating with the teams myself but we all know that it's going to be accelerating during this weekend," he said in Monaco.

"I cannot say all the (announcement) dates for all the teams but I hope very quickly."