Alli has not played for Spurs in any competition since the 5-0 cup win over non-league Marine on 11 January, with the attacking midfielder suffering from a muscular injury.
Before that, the 24-year-old had fallen badly out of favour at Spurs, with his four Premier League appearances this term amounting to just 74 minutes.
He was strongly linked with a January exit, as Paris Saint-Germain – now coached by Mauricio Pochettino – were said to be interested, but a move never materialised.
Therefore he has been tasked with recapturing the form from his early days at the club – Alli's 63 top-flight goal involvements was bettered by only six players across his first three seasons in the Premier League.
He was proving a real weapon for Spurs in his role behind Harry Kane, and his 26 assists over the same period was the fifth highest in the division – Alli found such consistency despite being significantly younger than those he was competing with.
His Spurs career now appears to be at a crossroads, but Mourinho insists there is a way back for him.
"Dele trained yesterday with the team and well," Mourinho said. "Long time away, couple of weeks no training with team and recovering.
"Can he play tomorrow? Well, he's not injured but I'm not sure he can. Can he help us? I believe he can. In terms of having Dele on the bench to come for a few minutes to try to help the team, is that possible? I have to speak with him but I believe he can."
When asked if anything had changed for him to sound optimistic for Alli, Mourinho said: "Nothing changed. He's not injured. He's not injured, he can train with the team.
"He went through a process of not training and trained with the sports science people and then jumped to team work, which he did yesterday for the first time.
"Nothing changed, what maybe changed is the speculation around him because in this moment everybody knows that he's a Tottenham player and he doesn't go to any place. So probably the end of the speculation will be the end of the questions.
"He can train and he can try to help the team because this is what we want. It's what we need. We need players to help the team. Hopefully he can do that.
"In a normal situation he wouldn't even be considered for tomorrow, but with the injuries we have with so many matches we have, maybe we have to accelerate his process and maybe we can.
"But of course, I want him to be fully on board and to agree and that depends on his feelings. But if he can be on the bench tomorrow and to come for 10 or 15 minutes to help the team, that would be good for us."
Kane returned from an injury of his own in the weekend win over West Brom, getting himself on the scoresheet, and Mourinho confirmed the England captain got through the 90 minutes with no major issues.
"No bad reactions, he played well as you could see. No problems, at least no big problems," Mourinho added. "Again, we need to go player by player, on two days between West Brom and Everton, we go player by player to have their feelings and discuss with them to see the best options.
"Of course, we want to go with a strong team [against Everton] but at the same time we don't want to create problems with the future of the players."