Blackpool boss Paul Ince believes Wilfried Zaha's ?15million move to Manchester United makes his son Tom worth ?25million.
Ince issued the transfer warning to clubs trying to prise his son away from Bloomfield Road.
Ince senior told the BBC: "If you're talking ?15million for Zaha, Thomas has got to be ?25million. If you compare the two, Thomas should cost more.
"Zaha is a fantastic player, don't get me wrong. Zaha's a stronger runner and does a lot of tricks, whereas Thomas is more direct, he makes things happen and he scores goals.
"You've got a kid playing in the Championship who has scored 18 goals. When you look at the leading scorers, they're all strikers, and he's there among them.
"Potentially, I think he can reach that value. If Palace want ?15million for Zaha who has scored six goals, it makes you wonder what price he's going to be.
"You're not going to get it because he's not proven in the Premier League, but if United are paying ?15million for Zaha, on the stats you'd have to say Thomas is worth a lot more than that. That's my opinion."
United hold a 15-point advantage over their rivals heading into Monday's derby clash at Old Trafford.
With just eight games remaining, Mancini has already conceded the title to United but the Italian is determined to cut the deficit to a figure he believes more accurately reflects the on-field gap.
Mancini said: "We don't deserve to stay 15 points behind.
"They have played very well, they have won a lot of games.
"The last 18 (unbeaten) - the last time they lost was Norwich.
"They deserve to stay on the top, but not 15 points. It is not a true table.
"Now we have eight games. If we play well, if we win a lot of these games, maybe we can reduce this gap.
"This should be our target in this moment."
City memorably thrashed United 6-1 when they visited Old Trafford last season. Mancini is certainly not expecting a repeat.
"This is impossible," he said. "This can happen every 100 years."
But he does expect his team to give everything, even though the title seems out of reach and they face Chelsea in the FA Cup semi-finals the following week.
He said: "If it is not important for the table or the title race, I think the derby is always a derby. It is important for us and for them.
"We have pressure, always. It will be like the first (derby). I think every derby is important.
"We want to show we don't deserve to stay 15 points behind and we can reduce the gap from now to the end. "But the title race is finished."
City go into the game on the back of an encouraging 4-0 thrashing of Newcastle and boosted by the news key midfielder Yaya Toure has signed a new four-year contract.
The influential Ivory Coast international has committed himself to the Etihad Stadium until 2017, ending speculation he could leave in the summer.
Mancini said: "I am happy because Yaya, for me, is one of the best players in the world and we are happy he plays for us and he stays here for another four years.
"I think it is very important for the club."
Toure turns 30 in May but Mancini does not see that as an issue.
The Italian, speaking at a press conference to preview Monday's game, said: "I think that Yaya is a player that can play until 36, 37 because he can play in front of the defence, like a central defender.
"I think he can play every position. I think when he is very old, like me, he can play as a defender."
Toure's agent had claimed last month that the player - who still had more than two years remaining on his previous deal - was growing impatient over the delays in reaching an agreement and issued an ultimatum.
Dimitri Seluk threatened to start negotiations with other clubs if a deal was not agreed before the end of March but City were always confident talks would be concluded satisfactorily in the fullness time.
Mancini said: "We are only happy that he continues to play for us and has signed another contract.
"This is important for me, for him, for the club, for the players."
Playmaker David Silva signed a new five-year contract earlier in the season and Mancini expects more deals to be agreed with existing players in the coming months.
Two that could become a priority are Carlos Tevez and Gareth Barry, who will both enter the final years of their contracts in the summer.
Mancini said: "We have time to talk about this.
"Yaya was important - also for the other players it would be the same, in the next month, next two months. I am confident."
