Everton midfielder Francisco Junior is training with Celtic ahead of the January transfer window.
The 22-year-old former Benfica youth has only played once for the English Premier League club's first team since joining in February 2012.
He had a loan spell earlier this year under Celtic manager Ronny Deila when he was in charge of Stromsgodset.
Deila revealed on Friday he has yet to decide whether to extend Junior's trial period.
It is believed that Everton could be open to another loan move, or even a permanent transfer.
Midfielder Junior was born in Guinea-Bissau but played for Portugal at under-19 and under-21 level.
|Celtic manager Ronny Deila on Virgil van Dijk|
|"Virgil is developing here, he's doing better and better performances, he wants to stay here."|
He was sent on loan to Leiria while with Benfica and also had a trial with Manchester City before joining Everton on a free transfer.
Meanwhile, Deila revealed his January signing plans are at an "advanced" stage.
The Norwegian said: "On 1 February we hope to have a better squad than we have today and that's two things - keep the players we need to keep, the best players, and we have to get some people in.
"It's what's available but the most important thing is quality, we need quality players. If we can buy quality players we will do that [rather than loan them]."
Deila also said there have been no new developments in Kris Commons' contract stalemate, and reiterated his hopes to keep Dutch centre-back Virgil van Dijk.
"Virgil is developing here," Deila added. "He's doing better and better performances, he wants to stay here.
"He really enjoys being here, in training he is smiling. We want to keep him and if something is going to happen with him I hope it's the biggest clubs in the world that's going to do it. He's a very good player."