It means Guildford, who returned home to Napier from French club Clermont and is representing Hawkes Bay in the ITM Cup with a view to making a return to Super Rugby, has every reason to play well in Pukekohe next week when the Magpies take on Counties-Manukau.
Umaga is in his last season as Counties' coach before taking on the Blues and is on the lookout for 12 players to add to his Super Rugby squad. Counties host Hawkes Bay a week on Friday.
"We are considering him," Umaga said. "We need to do our due diligence on everyone and see who is playing well. We're looking at everyone in the ITM Cup at the moment."
Asked what he thought of Guildford's form on the wing for the Magpies, Umaga said: "I've seen a couple of games and we play them soon for Counties - he's going well. It's what I expect from a player of his calibre."
Former All Black Guildford was close to signing with the Waratahs to link with former Crusaders coach Daryl Gibson for next season, but had second thoughts about a move to Sydney, saying he wanted to stay and fight for a place in one of the five New Zealand teams.
After his move from the Crusaders to France following his well-publicised battle with alcohol following the 2011 World Cup, he has little chance of returning to Christchurch. The reigning champion Highlanders are unlikely to need another wing, and the Chiefs and Hurricanes appear to have a settled squad - which leaves the Blues.
New Zealand Rugby chief executive Steve Tew said Guildford's return to Super Rugby hadn't been discussed by his organisation.
"To be honest, I don't think we've given that any consideration or not," Tew said. "I don't know that he's on anyone's list but he might be."
"I suspect that there are, in most of the Super teams, still three or four slots available in the squads and certainly in the wider training groups," added Tew.
"The Blues are still looking for a number of players so I would've thought Zac, and any number of players, are playing over the next few weeks with the possibility of a professional contract in this country."
All Blacks analyst Alistair Rogers has been appointed by the Blues as their new defence and skills coach. It is understood that Rogers, a Welshman and former professional player, has been on the franchise's radar for some time.
"Coaches and players who have worked with him spoke very highly of him and and about his knowledge and detail. It's an important area and I wanted a very specific person. He fits that profile," Umaga said.
The Blues' final assistant coach - in charge of the backs - should be announced within a fortnight.
